10-15mm I think. Whatever the usual high tensile steel ones are that come with disc brake calipers ? They usually have a built in washer type thing. Went round a few bike shops and none had any so would be mega if you do
I'll check my parts box and get back to you, for some reason I ordered 6 bolts for a caliper that I only needed 2 bolts for. I can't remember the length though, I suspect they're a bit longer than you need!
Looking good! Do you know what length bolts you need? I might be able to help.