Are you after main cap STUDS [recomended] or main cap capscrews [aka bolts]?

By using a sample main cap capscrew you can measure out the length & add a suitable amount for a nut & washer. Naturally you also need to measure the diameter & the existing threadform which will be a standard metric size anyway.

With these dimensions it may well be possible to select a suitable stud from their range.

I have main cap studs but
A. I cant find then after a quick 'blokes' look.
B. I have not yet fitted them to confirm that they are the correct ones.