This may be a bit late, but if you are still looking, see link below for where to buy blank aluminum sheet. I made a new chassis for mine and it's far better than stock. The stock is made from 6061-T6; my new one is 7075-T6 (aircraft alloy) and it's nearly twice as strong.

http://www.onlinemetals.com/merchant...916&top_cat=60


Picture below...