A few places to look around:

www.jettengineering.com Dub Jett makes race engines and high performance sport engines, plus accessories like mounts, tanks, etc. His "crap trap" series of articles are good reading. I use Dub's square mount for my TTPro .40 on the 424 plane.

www.darrolcady.com Darrol supplies a lot of stuff to racers, his website has good info in it.

www.pspec.com Performance Specialties (Dave Shadel) - Dave did sell the Nelson engines, accessories. Not sure what's there now, but again, good information if you dig around his website.