For the power amp section, any decent 6L6 tubes will do. I think I was using some from Electro-Harmonix as a replacement for the Fender Groove Tubes (which are actually just a re-brand of other tube makes) and they sounded quite good. If you're looking to spend a little cash you can go for the SED Winged "C" 6L6 tubes which I remember Alan recommending:
http://www.thetubestore.com/Tubes/6L6-5881-Tube-Types/Winged-C-SED-6L6GC
One thing I would
definitely recommend is switching out the V2 pre-amp 12AX7 tube with a 12DW7 (I got one from Mr Valve, don't recall the brand). To my ears that did a lot to tame the harshness on the drive channel by lowering the gain and just making it sound a little smoother. The Hot Rod has so much gain anyway that you can still get very saturated tones out of it if you want.
Finally, there are a number of guides which show you how to re-bias these amps yourself (takes about 15 minutes once you know what you're doing) and all that you need is a multi-meter. Just be very careful and employ the so-called "one hand rule" and you won't shock yourself to death. ?