I seriously doubt that camera manufacturers buy off-the-shelf for the same reasons you and I find it unsuitable. Assuming you don't want to cannibalize old Burke & James cameras, you're left with two choices. The first is to go to a CNC machine shop and order 100 of each piece you need (or whatever their minimum/price break-point is). The second is to set yourself up with a mini-lathe and make your own parts. There's no easy solution unfortunately.