Quick FYI-You don't have to resin the piece before Fiberglassing it. I did that with my first fiberglass job, and there is no warping to speek of. The trick is to leave the more important support struts in, then add some fiberglass to the main stress points in the piece. for helmets, that always around the visor. Then, once thefiberglass and resin is dried, simply remove all of the support struts, and go from there. its worth it, and saves plenty of time.
Either that, or simply go the Smooth-cast 300/320 way. They sell that stull here in Canada. But, I highly recommend if you live near the USA/Canada border, buy it from the US. Unless a store that has it is close by (within driving distance), but from the US. Its far cheeper.
Also, I have found Resin and Fiberglass in the following stores in Canada:
-Canadian Tire
-Wal-Mart
-Home Hardware
-Almost any Auto parts/Autobody store
-If you have a Tecx. Program at your school, you can grab some scrap fiberglass from there for free. Just ask the teacher first.
Good luck with the armour.
Cheers!