In BTC? In USD?
CMC has it, why look elsewhere? https://coinmarketcap.com/currencies/namecoin/
It's possible to see historical Namecoin's price chart on NMC Watch, the link provides price chart from June 2 to current date.
Most links above are dead... I'm looking for historical pricing of Namecoin in 2012 and 2013. Seems like most sources start in April 2013 while the coin was introduced in 2012 (correct me if I'm wrong).