That particular circuit is based on the "Firefly" project which is derived from the AX84. Look around for AX84, you'll find their forums, links to suppliers, kits and way more. The host of their forums runs his own store, doberman amps I believe. I was able to cobble together my own independent tube reverb as well.
Tubes are fun and simple. It's easy to understand what the circuit is doing. Just be careful and follow the safety rules especially regarding the high voltage caps.
Building that amp was a very rewarding project. It's all mine, and I was even able to re-use some vintage tubes my grandfather (an old tv repairman) had given me. It's really a shame I'm not a better player