They are all easily available tubes. I have done business with The Tube Store: www.tubestore.com and was very satisfied with their service. They carry online all the tubes you need. The 6C33C, 6H30P, 6N6P (or 6H6P) are all russian tubes that don't have western equivalent (if I am not mistaken), the ECC83 is a 12AX7, a very common tube. The Electro Harmonix, Sovtek and EI are very good as modern tubes go, but if you are interested in going the NOS route, the sky is the limit: Telefunkens, Amperex, Mullard, GE, you name it, tube roller's dream. If the ECC83 is the input tube, it will be probably the one making the biggest difference in final sound, so the most important.
You could also contact a store in Montréal, Canada called Coup de Foudre: www.cdfaudio.com (514) 788-5066. Some of their technicians are former employees of Tenor, I think the designer himself works there. I am sure they can provide some good information.
Hope this will help you.
Serge
Montréal, Canada
