Just steal them from Hobby Lobby. They don’t have anti-theft towers or LP.
Edit: also if you want a nice back patch but the band you like doesn’t make them you can buy a T-shirt, cut the graphic, sew it on, and go over it with clear nail polish or something similar and voila. Or you could staple it on if your hand starts to hurt from hand sewing a whole back patch on, not recommended but it’s what I ended up doing when I was a punk kid.
Edit edit: You can also fill in empty space with safety pins, they look edgy but they also serve a practical purpose if any of your patches (or someone else’s) start to come off.
You’re not gonna be able to find Blowback anywhere online unfortunately :(