That was my amplifier, and I got it from Frank Stuppel who has unfortunately passed away since then. He was a really nice guy and brought together a group buy for those amps. I think they're still available directly from the manufacturer.
I built that amplifier from the kit and wrote-up the assembly process in the link below. I'm still running that amp and driving those speakers, by the way. I've upgraded the tweeters in the speakers, but other than that, it's the same system I built back then. I've used it regularly, several hours a day and it sounds great and hasn't every needed any service.
I really like my little Stoetkit. Makes a very nice bedroom system. In its price range, I don't think there's a better tube amp kit. It looks good and sounds good. The only downside is they're tough to get a hold of.