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!