Hi Chris,
Currently, if you want to define each Buy Now button to direct to a diffrent source, you would have to build the store with dynamic pages, and set up the logic in the database and connect it to a button.
If you want more info regarding that you can find help in the Velo Community:
https://www.wix.com/velo/forum/community-discussion
Note, you can also set up the store to work with other diffrent platforms (e.g. FB, Amazon etc.) see link here:
https://support.wix.com/en/wix-stores/setting-up-sales-channels