I don't think the original TruffleC is available anymore. But TruffleC evolved into the GraalVM LLVM runtime. We're now running the C programming language on GraalVM indirectly, by compiling it to LLVM bitcode first. The core idea is still the same from back then, but it's a lot less work to implement.

The code is available at https://github.com/oracle/graal/tree/master/sulong