BNR34 Brembo replacement pistons

[MrAceman]

Turns out I need the rear pistons for my BNR34 Brembo calipers after all.

I can find the front caliper piston part numbers... in case anyone needs them:

41121-12U00 x 4
41121-12U01 x 4

But I can't find the rear piston part numbers. Can anyone either help me out with the number or teach me how to look up part numbers in FAST?

Thanks!