I hardly imagine that all the magi of a covenant have to go themselves to harvest all the vis each year, especially in a large Tribunal like Novgorod. Can they "prepare" a vis source to be harvested by a companion using a mundane method? Do they have to create a magical artifact able to do this and give it to the companion who will harvest? How does it work generally?
The campaign I've played years ago didn't touch that subject, You had X vis points/year of that type, and you had them automatically. But I think this may be interesting to play too.
This all depends on the specific vis source.
Some sources can be harvested by grogs after a thorough initial survey by the magi, some require grogs with the right enchanted devices to identify and/or gather the vis, and yet others require magi to be prepared and ready to conquer the vis every time: from competing magi, dangerous faeries or others.
It all depends on what you want to spend time and energy on in the saga.
It requires magi, specialists with supernatural abilities, or grogs with relevant devices to find the vis sources and learn how, what, when etc. it can be harvested.
IMHO you can delegate subsequent harvesting to dependable grogs, unless the SG wants to make it difficult for some reason - maybe to spin a story off it.
Vis source requires as much as effort/time/investment from the players as the story needs.
If the vis can be harvested by the non-gifted, it can. Some vis can't be.
You can certainly have vis manifest in places magi have some or great difficulty accessing. The Corpus vis that appears in the bedchamber of the Duke is best acquired by a member of the staff. The Auram vis that appears on the peak of Mont Ventoux may be harvested by Redcap. The Herbam vis lining the heartwood of the elder oak of the forest can be accessed by cutting it down, or by a mage leaching it out so the oak may live and produce more vis.
(The agents mentioned above may well expect some payment or service for their harvesting, of course.)
Caution: I've sometimes found the result of vis harvesting not worth the effort.