The fan that comes with the TRUE Rev C 1366RT is the Thermalright TR-FBD1600, which I believe is sourced from the same oem as Scythe gets the S-Flex SFF21F fan from. The fans have the same exact specs and they look almost exactly the same. If you want to run with a push-pull setup, just get a SFF21F to go with the stock fan, along with a set of wire clips or another plastic fan mount. I would buy from someone besides those 2 vendors though, where you can get a better price most likely. Such as Sidewinder Computers or Jab-tech.
BTW, a push -pull setup will only net about a 2-3 C improvement in temps, in my experience.