I think this is a list of all the vis sources suggested so far, with comments and additions in blue
Creo:
Harvesting maggots from animal carcasses in the summer. I like this one. Perhaps this could be something we have to search for all summer in the temple area or in a nearby woods where a low magical aura occurs. If the maggoty carcasses need to be searched for this could be a way to get some of us off-site to get a story started.
Harvesting an apple tree that contain creo vis in the apples, the tree only produces 6 apples each year and three of those must be allowed to fall and rot. This is okay as well, although I think I like the maggots idea better.
Water poured on the altar stone of the ruined temple contains 4 Creo vis in the Spring. Already on wiki
Crone’s menstrual blood I think this may be more trouble than it's worth.
Fish roe gathered from a shallow pool. (Need to think about the story behind this more.)
Intellego
The Tree of Truth: A tree that contains an odd fruit not common to the area that can be harvester for Intellego vis. Okay
Alternatively The Waystones: Basically follow a bunch of waystones, from each waystone one more will be visible and when you reach the final one your shoes will contain intellego vis, would be suitable to the hilly terrain of the area and is a bit different than having another tree. This one always feels more like it should be in the Stonehenge tribunal.
Condensation on one of the windows in the covenant library contains Intellego vis. Investigation revealed that the stones forming the frame came from the stones scavenged near the ruins. Attempts to duplicate the effect have proven fruitless up to this point.
Muto
The Chrysalis of Rebirth: Each year a bunch of caterpillars nest in a field of wildflowers a ways off form the covenants, after the butterflies burst forth there are leftover cocoons that didn't hatch that contain muto vis Typical source, but still a good one.
Perdo
The Stone of Death: During the second week of june the stone is shrouded in a light mist, if an animal is sacrificed each day for the ten days this occurs then perdo vis forms from the blood I'm not sure the attention we might get from a blood sacrifice is worth it.
Water poured on the altar stone of the ruined temple contains 4 Perdo vis in the Autumn Already on the wiki.
Rego
If the leaves from a laurel tree growing out of a Roman ruins are woven into a crown on midsummer, they contain 4 Re vis Aready on the wiki.
Still need another source for this one.
Aquam
Aquam vis is gathered from a tidal pool a half-day's journey up the coast. The water that remains in the pool at the low tide of the first new moon in Spring contains 4 Aq vis. Already on the wiki.
Corpus
I believe ghosts were discussed Would we need the "Haunted" hook for this one. Or perhaps the ghosts are a bit further off. I'm okay with this one.
Hangman's Oak: Decade's ago a man was found guilty of murdering his wife and a wandering monk, he was hung on the largest oak tree in town, since then each year a guilty man is hanged from the oak the tree produces one blood red acorn that contains corpus vis, only one acorn is produced regardless of how many men are hanged, can become tainted if the man was innocent. Seems a bit iffy to me.
A pool located in the covenant regio contains Corpus vis after someone bathes in the water. (2 pawns per season)
Herbam
Mallorn Dandelions: A hill outside the covenant with a small faerie aura grows thick with dandelion blossoms each spring, if left to age until the winter solstice they contain herbam vis Okay.
Mentem
Howling of the Winds: Basically strange faerie magic, centuries ago a faerie was killed by her son, taking another mother to that shore at some point in the year leads them to sob uncontrollably, harvesting their tears contain mentem vis I like this idea. It also give us a slightly different flavor, is we want to keep the faerie story. I would suggest the base of a nearby cliff as the location.
Terram
The Rock Shepherd: A rock elemental fell in love with a water elemental, one day he found the water elemental had dried up as a result of a human mill, each year at the end of winter he takes a pilgrimage and places one of he best rocks in the empty stream, the enxt day the rock can be harvested for both aquam and terram vis, which works well for us. I also like this one. Would the Rock Shepherd be someone/thing we could develop a relationship with?
Still need another source