Bike shops are out of a lot of things, but I can't imagine they don't have brake mounting bolts at any local shop. (But then, there's a lot of things about this latest bike boom I thought I'd never see, so...) I guess it depends how particular you are about the bolts you get. I'm sure the OEM bolts Shimano supplies (
https://cambriabike.com/products/shimano-xt-m750-739-v-brake-mounting-bolt) could be a little rarer, but if you just need to mount the brakes, it should be pretty simple. (These Shimano bolts may be what Garth's link refers to, but I can't seem to get it to connect).