Where do you guys buy tubes?

Hi, anyone familiar with 6N1 and 6P15 tubes? I bought an  inexpensive hybrid amp for a small system and would like to try different tubes. Being a tube preamp stage only, I'm not expecting alot of change, but thought I'd ask.

If you're familiar with these tubes I'd appreciate your input. I'm emailing some of the guys already mentioned in the post, fwiw.

Thanks in advance