Brake is rubbing agaisnt wheel but the brake adjustment screw fell off or isnt there, do bike shops sell these? Or any other way to adjust the brake gap

That rusty thing is the brake adjustment screw. It might take a fair amount of time with PB blaster to get that one loose, but maybe you’ll get lucky. Don’t get any PBB on your brake pad or rim.

~~Probably a 4mm allen~~