They were originally made by Vashon, which was later bought out by Estes. I have one of the Valkerie models, which belonged to my brother and was flown only 3 or 4 times. One of these days I plan to restore it and fly it again, just because it's so unique. The rocket consists of an aluminum "motor" (actually a propellent tank) with a nozzle at one end and some kind of thin disk thingy on the other end. Forward of the motor there is a short length of very thin-walled aluminum tube, then about 4 or 5 inches of cardboard tube, and a styrofoam nosecone. Everything had to be extremely light on this rocket because the performance is lousy compared to regular Estes black powder motors.
There's a small pin with a loop at one end which locks a plug into place in the nozzle. A string is tied to the loop of the pin. To launch, you pull the string and the plug is released. Since it's non-pyrotechnic, you can do this from right next to the rocket.
The stuff that has replaced Freon can be used in these rockets, though the performance may be slightly lower.
If you wanted to clone one you would need to machine the motor and other metal parts. Not really worth the effort, IMHO.