Your talking some big bucks to get them. The company is called unlimited engineering. Most people run their aluminum chassis, braces, bulkheads, and bulkhead braces, and rpm arms. The company does not make much any more but the guys on the
http://www.traxxas.com forum have a stockpile. Other than there I dont know where to get them. UE does not have to much on the website but here it is.
http://www.unlimitedengineering.com/cgi-bin/store