I just emailed the folks over at Mexican Radio regarding their black beans (which are vegetarian but not Jain). Note that their kidney beans are not vegetarian.
Not even 10 minutes after I’d submitted the information request, I received a phone call from their offices in upstate NY.
The final word: they can prepare the beans without onions or garlic if given enough notice.
The next move is to request the same be done for salsa and guacamole (upon special request, of course) and I’m all set!