I have the Fire Bottle 6L6 as well and would like to try the KT77 and 6N23P. Can you recommend a good source for those tubes?
There are plenty of the 6N23P tubes available on ebay. Those are the easy ones. A guy in Washington State has created a bit of a buzz/possible mythology with his detailed testing and review of 6922 type tubes. Among the Russian 6N23P, he claims the best are specifically 1975 gray shield, single wire getter post from Voskhod plant ("rocket" logo) and the 1974 silver shield SWGP from Reflector plant. I don't know how true this is, but the price difference isn't great, at least for the 1975 rockets, so that it is worth it for the peace of mind. There is at least one ebay auction right now for three of these these: #161771267407 for $57 shipped and one for two 1974 gray/swgp: #231613856699 - $49 shipped. There may be others.
For the GEC KT77's, you have to keep an eye out to find good deals. I have gotten some on ebay for as little as $200-$300 / pair and they have been fine. Just make sure there are test results posted, good seller feedback, etc., as well as returns accepted. You can also find a pair from a reputable tube seller, Brendan Biever of tubeworldexpress.com for $650, which is the typical market price for good examples of this tube. There are a few listings on ebay, some of which are very expensive. There is a quad of Gold Lion labeled, testing as new, for $1600. Best offer accepted, so you might get them for less than that, but more than about $1300 is getting high for a good quad.
For the KT77's, the buzz is that short brown bases are preferable to the bigger black bases. I have a pair of each and can't tell any difference. I've also heard that the ones labeled Gold Lion are preferable, but I don't think there is truth to that either other than they look cool. Be wary of "Gold Aero" though. I can't find anything definitive, but have heard that these may not be authentic.
As an aside, I bought some "tube saver sockets" since I've been rolling alot. They are just like tube bases, but you can plug tubes into them. They plug into the inspire's sockets and don't move. I swap tubes in and out of the savers, so I'm no longer worried about wearing out the sockets installed in the amp.
I don't recall if I've seen you over in the big Dennis Had Inspire thread I started a while back on audioaficionado.org in the Cary section. It's almost at 900 posts and has lots of folks with these amps.
PS: I guess this is a bit off topic for a thread on Class D amplification - sorry about that.