Most of the 405th would tell you to make it yourself, unfortunately. I've been over there for about a year and that is typical of their responses.
What kind of Halo Armor are you looking for? I would suggest the Halo Combat Evolved low-detail armor. It is an easy pepakura file, can scale nicely without losing much detail, and looks nice.
I can look into how much it would cost to make, if you would like? Basically, it would be pepakura'ed out of 1mm sintra (for added strength) and backed with smoothe on (non toxic plastic, rather than fiberglass).
Are you just looking for the armor or the armor and helmet?