I've been desperately looking around for parts to rebuild my Brembos and could not find much information anywhere, nor parts with reasonable information.

So if you ever need to replace your piston seals and boots, note that the CARLSON 41285 kit will do the job perfectly.
Ohio Performance Solutions also sell these.

Each caliper has 4 equal 38 mm pistons. So should you ever need to find parts, this is the dimension you must look for.

 

ZZP sells all the individual parts of the Brembo calipers as well.