I picked up some scraps from a construction site. Ther was quite a few short pieces of PVC that had been cut off and thrown away. The 6 inch pipe can be cut and made into just about all of the armor you need, you just cut it out using the WOF templates and then heat them up to flatten them out. The back plate is about the only thing that is too big to get out of a 6 inch pipe. If you find some 10 inch pipe being thrown out you can cut out a back plate, I think a 10 inch pipe has like a 22 inch circumfrence.
Some times I have had to clean the mud and rocks off of the pipes before they are ready for use, but I have had good luck with it. The other thing that I have done is to go by sign shops and ask for scrap sintra I have had good luck with that too.