Commerce doesn't support multiple stock sources out of the box but you might be able to work around it, depending on your requirements.
To expand on your thoughts...
How are your products set up? Commerce doesn't add a product directly to a user's cart, it's actually Purchasable—with Variants being one of the purchasables in Commerce.
If your products don't have a lot of variations that you'd use a Variants for, one way to pull off what you're trying to do is just filter variants based on the user that's logged in—creating multiple groups could be one way.
That way, you could take advantage of Craft's native stock-handling features directly.
Depending on how many products are in the store, you might also choose to use something like a CSV import/export and not touch the Commerce backend directly.
Multiple stock level fields
Another slightly cleaner way to pull this off would be turn off Commerce's native stock handling (set it to unlimited) and roll your own validation with your own inventory fields.
From a code standpoint, that's a more intensive way to go but it does put you more in charge of how you handle inventory. Commerce provides multiple events to let you handle the stock validation and it might be a good way to go depending on your rules (eg you might want to reallocate inventory from a trade customer to handle a regular customer in some cases or vice versa).