The graybeards of model rocketry, and many younger fan-atics, will undoubtedly know more about Vashon and Estes Cold Power rockets than I, and I won't make this a tutorial. These rockets/motors still pop up on EBay and Wes "Dr. Zooch" Oleszewski has several. Wes is a regular at MDRA and flew them several times at this past weekend's launch. He flew them in his Mark II kits and the performance was quite impressive, probably equaling 'B' impulse. He used readily available airbrush propellant and painted the bottle flat black to improve performance.
He also took the time to explain to me how both the Estes (which he prefers) and Vashon varieties work. I can't remember the Vashon details, but will recount how the Estes ejection works. This is pretty cool. The top of the motor has a rubbery insert with tabs that fit through the motor's wall. You slide a spring powered plunger over the motor and, when the motor is pressurized, the rubber tabs bulge out and old it in place. As the propellant is expelled, these slowly release until the plunger lets go and pops the 'chute. He says they go for about $150 so they aren't cheap. If you bid on one, he warns to ask the seller if the rubber tabs are cracked and if the trigger release on the launcher is operational. If the answer is 'no' and 'yes', in that order, then it is a good buy.
If you want one, I'd recommend contacting Wes. He's always willing to help out and really knows about these things. While you're at it, order a Mark II to fly your new Cold Power motor in.
PS - Here's a good thread on the good Dr's efforts.