I love the little compendium about mundane beasts that exist, but I wonder in which books I can find more mundane animals or will you publish a book with many more beasts and animals?
The final version of these rules ended up in Realms of Power: Magic, and includes many magical animals. I don't think we'll ever get a bestiary larger than that!
Well, plenty of books have one an animal or two here and there.
Magi of Hermes has stats for Asp, Bat, (dromedary) Camel, Crocodile, and Lion
Lords of Men has some stats for as pets like (magpie, squirrel, and monkey) as well as advice on customizing horse and dog stats to represent specific breeds common to the medieval period.
The Cradle and the Crescent gives stats for the Hyrcanian Tiger and Steppe Pony as well as giving advice on tinkering with stats to approximate Bactrian Camels, Arabian Horses, Saluqis and various types of Falcon.
Legends of Hermes has Large Fish, and Large Shark.
I think that's it for now... If you'd like, however, I wouldn't mind trying my hand at some animal creation at your direction (I've not had much opportunity to do so of late).
HoH:MC has extensive rules for creating mundane beasts in the Bjornaer section, with some pretty good summaries of how specific animals might be put together. They aren't 100% complete and ready to go, but it's pretty quick to go from those thumbnails to a full version and you can usually fudge what isn't spelled out if in a pinch. You should be able to generate any mundane creature without too much difficulty even if it isn't covered in any other form or place at all.
IMO, the rules there don't mesh completely cleanly with the rules for magic animals in RoP:M as the magic animals aren't built with the Qualties type mechanism that the mundanes ones are constructed with but rather have Magic Qualities and Inferiorities that must be balanced out like a normal character's Virtues and Flaws (which they also have). It's a little muddy trying to make, say, a Polecat of Virtue because of that, since you have to figure out how to replicate the Qualities you really think it needs to be an especially polecat-ish polecat under the slightly different system.
I'd love to see an expanded "Mundane Bestiary", maybe a 64-page softcover like "Apprentices". Alternately add some stuff and make it a "Familiars" supplement. Either way, a revised version of the 4th edition "Medieval Bestiary" would be a good thing.
Two good ideas - the Bestiary including the creation from HoH:MC and many animals and beasts from Sourcebooks. The Familiars Book can be great too. And both can be good near on pages to the Apprentices.