Might as well post some random guides, and people can pick out what they want.
- If you think you are that pro at sculpting.
- Dandy little guide that begins with sketching out the pattern.
::Craft Foam Armor
- This link will pop up a LOT all over the web. I hear generally desirable results, though I do hear some hate for it. I want to try it but haven't yet.
- Durable alternative. You'll need a heat gun.
- Wigs, supplies, etc. Even some costumes to buy (though what's the fun in that?)
- Look around for something similar to what you want. You can always alter.
But just general advice - Look around your local store or even your house and see what all COULD be useful. Scour this site and other sites, such as Youtube, for how people do things. Even if it isn't EXACTLY your armbrace, you might be able to learn from how they pieced together their own pattern.