Where do you guys buy tubes?

For factory matched new power tubes like KT120s and KT150s I've used reputable (100% ratings with thousands of transactions) Ebay dealers with great success (Upscale lists stuff on Ebay also), and have bought matched signal tubes from "thetubestore" (new and NOS) and Upscale (NOS). Most have been fine, although some Psvanes from Ebay were bad…oops...

Tube World for rare exotic NOS!

No regrets ever!

On seeing what you want and what it's for, I second Ghosthouse in suggesting that you get them from ARC.

McShane and Kevin@Upscale.  However, two that I'm currently using were eBay.

WOW!!!! Andy from Vintage Tube Services is a super super nice person.  Helped answering all my questions even he don't carry the tube that I am looking for.  If I am looking for NOS in the future, this is the place I will do business with.  Two thumbs up for Andy at Vintage Tube Services.