Yeah I'm aware of the build mirror, but crashcart builds things under a different prefix so it must build things from source each time. I realize this doesn't affect most users (which is why it takes a while for disappearing sources to be found and fixed). A content addressed mirror for sources as well would solve the problem nicely.
It might be related to using a different Nix prefix for your builds, which is a little poorly supported. Just curious: Why are you using a different prefix?
