Are you looking for finished helmets or raw casts?
I got my MMPR Red from Aniki. You should check him out on Facebook. He has Blue as well and seems to have helmets for just about every single Power Ranger ever made.
Be prepared to wait around four months to get one though.
I have them all but the blue one. I can PM you the files. Note: I did not unfold these files. I got them for free from a different post. So if you build it, just give credit to who unfolded the pep files.