Painting bolt heads
Ill throw my hair brained idea out there.
I was thinking of rust blue. Check out rust blue for firearms. Even if they are blued, they can be painted over, and the chips wont look so bad.
Rust blue looks just like a phosphate finish.
This is what I used for a couple of rifles, and they never rusted after being blued.
There are quite a few coatings that would probably work well. And honestly, if you sent a gunsmith some bolts already blasted, it probably wouldn't cost too much. Most of the work with the gunsmiths is in the prep. But prepping bolts would be super easy.
This is what I used for a couple of rifles, and they never rusted after being blued.
http://www.laurelmountainforge.com/barrel_brown_inst.htm
Here is one rifle I did over the kitchen stove: