If you have at least three silver symbols you can bet BP with a man in the battle frontier. By battling in the structure he tells you (if your battery is dead I belive he only chooses Battle Tower Singles, but I'm not sure on this), you can get up to 15 additional BP per seven defeated trainers. If your only goal is to get the 48 BP for conter this might take longer, due to having to battle and defeat three frontier brains, but this would allow you to get BP faster for possible future projects.
Don't have any silver symbols :/ I would attempt to get 3 for this, especially since my battery isn't dead, but I really only need 48 BP haha, I'm not trying to set this up for future projects, so I'd probably get 48 BP just from getting the 3 symbols anyway. So far the Factory is still the only place I've been able to reliably get some, I guess I'll just grind it for a few more hours :/ This makes me appreciate how easy it is to get BP in Gen 6-7 haha.
Thanks for the answer!