A couple interesting things:
As a young man (I must have been 12 or 13) I "worked" for Competition Models. I put the kits together and in return for a couple hours work, I got a kit. Most of the time it was one of the Stardusters, but I also got a SST,
The reason the kit and plan are so rare now is that Competition Models was very picky about the quality of the balsa put into their kits. I would help Sal Taibi cut strip wood and he would throw out more wood than he would put into the kits (no exaggeration) They had a great reputation for contest quality wood.
And, the SST, in particular, had a boat-load of wood in it.
Most people would buy the kit, take the wood out, use it for other projects, and throw out the box and plans. Ray VanDewalker and I had the only two SSTs' that I've ever seen completed.