I got it from the official github,https://github.com/vinced/namecoin
Its the 3.21.91-version I downloaded as source, unzipped it
switched to "src"-directory
and compiled with
make -f makefile.unix -j 6
this needs a few libraries installed, but it keeps on telling you whats missing.
afterwards i copied the namecoind-binary to /usr/local/bin
created a simple config in ~/.namecoin/bitcoin.conf
(just rpcuser, rpcpassword, rpcport, daemon=1 and server=1)
and started up with namecoind
I'm running all my rigs on this one and already found some blocks - low difficulty at the moment!