You have to try pretty hard: the compiler and runtime are available in closed-source form for FogBugz For Your Server installations, in the Accessories directory.

I'm also planning on open sourcing the new Roslyn-based code generator. I don't currently have any plans to open-source the rest of it.

In the original blogpost, they (FogCreek) say they're going to go over and open source at least some of it in a follow-up post.