Is it? Do you have a page reference? I like Tremere!
Page 115, right column, second paragraph.
Just doing quick searches (pdf's are handy for that) for other Thebes related fluff and backstory for you:
From HoH:TL page 127:
House Tremere recruits cataphracts (Ghosts of mounted Roman soldiers of the East) were they can, and directs the remainder over the border into the Theban Tribunal, where they can harass the Latin invaders.
From ROP:TI page140 Infernal societas:
.. in what would become the Tribunal of Thebes.
The original Thessalians were reclusive worshipers of sinister gods of the underworld, they practiced sorcery, necromancy and could cast potent curses at their enemies. ...
They never joined the Order, and a small number of "Wild" Thessalians still survive in the region today, called the daughters of Erictho .. they dwell in the Cambunian mountains on the northern border of Thessaly
From HOH:MC p107
(not quote but summary) House verditus founder cult was descended from a pupils of the forge god Hephaestus based on the island of Lemnos. The house verditus home covenant is built on one of his forge sites on Sardinia in the Rome Tribunal but another of his forges is located 'in Yanartas, near the Antalya Gulf in Asia Minor, on the site where the mythical Chimera fell and where fire still leaps magically from the ground.
From Ancient Magic p52 Chthonic Santuries:
It talks about an example santuary dedicated to Hecate located in the Cambunian mountians of the Theban tribunal and goes on to say:
'One of the covenants of the Theban Tribunal, Erebos, has discovered the sanctuary. The magi of Erebos have not entered it because of the various traps set be the cultists of Hecate. The covenant contains several Perdo specialists, and they consider the cave their most important vis source.
...
The magi of Erebos may consider allowing the investigators access to the cave in exchange for assistance in resolving their conflict with the Daughters of Erictho.
...
The Daugthers of Erictho once used the sanctuary and consider the encroachment of Erebos just the most recent in a long line of trespasses. They have also come into conflict with Erebos and other covenants of the Tribunal of Thebes over certain magical resources.'
p87
Magi of Constantinople
Several covenants of the Tribunal maintain contacts of demesnes in Constantinople. These magi take a proprietary interest in the city and anyone venturing into it. One covenant Michael's Tabula, has actually established ttheir covenant in an abandoned mithraeum in one of the city's many ruined districts. Currently, the covenant numbers about a half-dozen magi, mostly from House Jerbiton. Long time time residents of Constantinople, they have little love for 'Franks'or any magi hailing from the kingdoms responsible for the destruction of 'the city'.
Thank you. Da Bear was helping me out with this post. I really appreciate that level of research.
With geocities shutting down soon, I've managed to get in touch with Jeremiah Genest and I'm working to get the material from his site to find a new home for it.
-Ben.
OK. I may be able to help find space on the Project: Redcap server if you need it. Send me a PM if that would be useful.
While not a tribunal book per se, Provence/Provencal had quite a bit sprinkled around in the main ArM3 book and in Mistridge. Probably a few others I've forgotten as well. It was the de facto campaign tribunal for 3rd ed I believe.
Rich
Well, by that standard the Hibernian Tribunal was written up in the 2nd edition Order of Hermes book, with all six covenants discussed.
Sorry for the necromancy, but does anyone know if this indeed came to pass? With my players partially stranded in the Aegean, I thought getting some inspiration for what the Theban Tribunal might be like would be a good idea.
Vrylakos
All I know is that GeoCities is toast and the old Theban Tribunal site went with it. 
given that Michelle has stated they aren't redoing any old tribunal books until they've covered them all, it's a pretty safe bet there's a thebes book planned. But when it'll be released is entirely a matter for Atlas, and they probably don't want to share that info.
Oh fiddle! That was a really amazing site. I wish that info could be resurrected somehow.
The Thebes Tribunal Book was, in fact, announced some time ago...
Ah, totally missed that!
Too bad about Thebes being later in the year. It would have come in handy now, but perhaps this set of adventures will whet their appetite for a return trip in future.
Off to Samos! Hm... I really need to figure out some sort of adventure to take place on Samos as part of the Initiation for the resident Mystical Fraternity of Samos member...
V
Wayback Machine?
I've been wrangling with Google's cached pages, but thus far I can't get geocities.com/leucretia/ypsoma.html or Y'psoma tes Pnoes tou Pneumatos to make an appearance. Admittedly, I don't usually mess with google's cached sites, so perhaps there's a way to gain access to this info that I'm unaware of.
Ah, thanks. It looks like the main page is there, but the meat of the site seems unavailable. I've tried clicking on them and also throwing the sublinks into the wayback machine to no avail. A pity - that site was excellent. Too bad the Deadfire Saga is also beyond the pale.
A nice poem by Yeats is on the front page, though.
Sorry, I've been neck deep in a writing project and so I haven't had a chance to get back to this post. I did grab the bulk of the site, I haven't gotten much mail from Mr. Genest, so I don't know if I can offer it to anywhere for posting. I'll check on it again. What I can do is zip it up and give it to you if you want it. Drop me a PM.
EDIT: I've just checked with him again for clarification, and as soon as I've got some kind of acknowledgement, I'll note it here. If possible, I'll bring the site (because I grabbed most of it, iirc) over to Sanctum Hermeticum...although it may need a little scrubbing. Nothing a little perl script or some script-fu couldn't solve quickly.
-Ben.
PM sent! Thanks very much for the offer!
Vrylakos