What we need, is an NPC, likely related to Thumbs, that will give you cooking ingredients to help bridge the fact that it's so difficult to get some of them. These ingredients would be more of the mid level ones, such as butter, or milk, where we can't get them too often outside specific encounters in a single area. This would help make bigger dishes a little more enticing to cook since the grind to get the ingredients wouldn't be nearly as bad as it is now. I would say they could give you like 5 items every time the Mole Market restocks, so lore wise, it ties in with Marvin being a supplier of goods.

What if there was a bovius you could milk

I don't think that a whole new feature and NPC is necessary. I think the main problem is that there are very limited sources for a lot of items, and a lot of those sources are even more limited in quantities (the mole market). How to fix this, basically ties into was Desnik is saying; Add milk as a drop from Bovius encounters, and add salt to Fishing. Simply make the items available through gameplay, and allow us to hunt for them and obtain them.

AND/OR drastically increase the stock quantities in the Mole Market and increase the amount of food items that stock at any given time. (Because I do see that they form an important pebble sink, so perhaps making them all too easily and readily available through gameplay could ruin that)

Perhaps the solution the issue lies in a combination of both. Both increasing the stock quantities and amount of items offered in the Mole Market, and adding the ingredients as drops in different parts of the game. Not with too high a droprate that you would never want or need to buy them after 5 minutes of grinding, but enough that it is worth the effort to go look for them.