The 501st doesn't endorse any makers themselves (technically we can't but that's a long complex discussion that will make your head spin), but that being said you can find info on good reliable makers here by reading around on what members suggest.
Typically your best choices range from FX, AP, TE2, ATA, RTMOD, and TM or Troopermaster. Anything else is very likely recast and may not be the best quality armor you can get and sometimes for even more money than the original armor its taken from for less quality. That's why we always suggest doing your homework and read up on the various armors as they all have different pros and cons to help make a decision on what armor is best for you.