All over the internet are 3d models, some in Pepakura form that are craving to be made. If you're not sure what Pepakura is, it is simply a program that takes a 3d model and makes it into a net so that the 2d parts can be printed, and assembled in real life. The viewer program which allows you to also print can be found here: http://www.tamasoft.co.jp/pepakura-en/download/viewer.html
The Designer program, which lets you scale the parts to you can be found here: http://www.tamasoft.co.jp/pepakura-en/
If you ever need help printing/scaling/anything with Pepakura, simple search the web (There are tons of tutorials for that) or simply ask me and Id love to help. Once you have the model you want to be foam (Keep in mind that you can find these all over the net by searching say "halo armor Pepakura" If you can't find what you're looking for, it most likely hasn't been made into a 3d model yet.
Ok, once you have the file, open it in the viewer and hit "Print". When all is done, you will have something like a pile of pages filled with polygons. Excellent, these will be your templates to trace on the foam.