The Sovtek 12AX7LPS is very good and not to expensive. There are a myriad of NOS tubes, but they are kind of pricey. Try a Mullard CV4004 from Upscale Audio.
http://www.upscaleaudio.com/Mullard-CV4004_p_5.html
http://www.upscaleaudio.com/Mullard-CV4004_p_5.html