signature keys

How do I find the public keys for signatures in the download.

For example:
  gpg --verify llvm-gcc-4.2-2.9-i686-linux.tgz.sig
gpg: Signature made Wed 06 Apr 2011 01:26:27 AM PDT using RSA key ID E95C63DC
gpg: Can't check signature: public key not found

But the key servers don't know about 0xE95C63DC