A volcanic hot spring is said to have incredible healing powers. Villagers and nobles alike come from miles around to restore themselves in its pungent-smelling waters, although locals caution them that the waters will lose their efficacy if bottled and removed. If magi investigate then they will discover that this is in fact true: it is the sulphur dioxide in the air which contain healing vis. Since the gas quickly becomes diffuse, harvesting it may require inventive use of Auram magic. If the vis is removed then the hot springs lose their healing properties for the rest of the season - worse, since there are large numbers of sick people wallowing in them, they can become actively harmful.
The mediterranean rim has long been the haunt of slavers. Christians are kidnapped for service in the Maghreb, just as Muslims are kidnapped and trafficked north into Christian lands. The stories that parents tell their children to warn them about slavers, have led to faeries taking on the role of slave raiders and traders. Recently, the covenant's agents have reported that a new band of slavers have begun offering their wares, mostly kidnapped children, for sale. These slavers are in faeries and the slave market takes place within a goblin market. Magi who are prepared to make war on these faeries may find themselves very popular, as well as gaining a windfall of Corpus vis from the bodies of the faeries they fight.
A local nobleman, famous for his sword skills and just as famous for his bragging, loses a hand in a tournament accident. Everyone - including him - expects this to be the end of his career, which makes it such a surprise when he turns up several months later with two good hands. At first he attempts to be mysterious about it, but he is unable to avoid boasting and soon the truth comes out: a wise woman, living on her own outside a large village, healed it for him. The Church makes plans to send an investigation to determine whether she is an agent of the Infernal - or just as possibly, an agent of the Divine. What if she's neither, just a hedge mage with strange healing powers and a stock of Corpus vis? If so, can the Order preempt the Church investigation? How will they treat her, and how will it affect the growing ranks of crippled people who've heard the nobleman's story and are planning to seek her out themselves?
(If you want something sillier, what if the nobleman himself is a vis source, harvested by removing his hands and other extremities at regular intervals? He would definitely resist such harvesting, and may ask his friends and liege for help. Kidnapping him is the logical choice, but would probably bring up charges of interference with mundanes.)
A local pasture is famous for its pretty flowers in spring, and many courting couples can be found enjoying the flowers - at least, that's what they say when their parents catch them. The wise women of the village advise their granddaughters not to lay down where the flowers are thickest, as sex there will result in almost certain pregnancy. Naturally, these flowers contain vis. If they are harvested, however, the young ladies of the town will find that there is no risk of conception anywhere in the pasture. This is a huge relief to them, and possibly to their parents who aren't ready to be grandparents yet. However, the relaxed behaviour that it encourages may alarm the Church, may invite demons, or perhaps both.
A spider whose abdomen is shaped like a human skull spins a web made of human bone and whose strands contain vis. The web accumulates a pawn of Corpus vis a season - or, if it's been left undisturbed for more than a year, two pawns per season. What is the mathematically optimal frequency at which to harvest it? If it's left to sit for several years in order to accumulate vis undisturbed, other forces may stumble across it: hedge magi, magical creatures, other Hermetic magi. What if, when the PCs first discover it, someone else already considers it to be theirs and is leaving it to accumulate?