Tube vendors.

the viva shop in mass is good, they ship quickly, communicate very well (sometimes a problem with andy at vts as he is older and essentially a one man show, as is jim m), viva is also very responsive when issues arise with tubes they sell

that said, i don’t believe viva does extra testing in house or burn in on their tubes, which can be quite important and valuable with some tubes for some amps... for new stock tubes i believe viva relies on the factory testing and matching, which for some makes and tubes may not be so great

I purchase new tubes from The Tube Store and NOS from Uncle Kevvy at Upscale Audio. Extremely satisfied with both dealers and shipping is about the same. 

As for me, Vintage Tube Services.

Vintage Tube Services for me.  Several purchases with reasonable prices and excellent tubes.  

I've dealt with Brett Jesse, Kevin Deal, Andy and Viva tubes on multiple 
occasions and have had great success.  I have also purchased 30 or 40 tubes from a local dealer in PHX that has been very good.  Dave at Arizona tube supply.  Very good.  I would say he seems to have mostly USA NOS tube brands, not so much on the European brands.  Great source.