When I deal with vendors I store them in a separate DB in an App. For example, I built a custom Shipping App where if the customer places a product in the cart from vendor XYZ, the shipping rate has to calculate the shipment from the vendor's address, not the Shopify one! So I present the merchant with a vendor editing screen, where they store all the possible info about the vendor for use in any transactions.
You could also use Metafields if you were so inclined. A Shop has vendors, so you could attach details to the Shop Object for fun and kicks.