My rear tore off after hitting a home made ramp wrong, i dont blame the car more my stupid idea and crap driving. In some ways these parts are supposed to break and pop off as less stress goes through the expensive bits. I did upgrade to the carbon reinforced set it only cost me £20 from Tonys Tamiya parts for A&B parts tree and new diff cups. My shock are the only things that pop off when i race but i have just upgraded to the aerated options damper that screw in rather than the ball joint, they also work now unlike the not so good plastic ones.
I mainly use Vellrip, in singapore and he ships worldwide, RCMart are ok but they take a while to ship. I usually order from vellrip on a Thursday night/friday morning if i have broken somthing on Thursday evening racing and every single order always comes the following Wednesday. good prices too and he stocks most Tamiya parts inc DB01 and the 501x.
Also try Tony's Tamiya Parts on ebay he's UK based and very good for most things and posts quick too.
http://www.vellrip.com/store/home.asp
later
VV