I've seen fair numbers of econojet SUs for sale by online vendors; the other Aerotech SUs are a bit harder to find though. Great-Lakes hobby, https://www.greatlakeshobbies.com/c...online-store/scstore/shophome.html?E+scstore, has the E30, F50 and G40 SU motors listed. Just Rockets, https://www.justrockets.com/, has D21, E15, E30, F50 and G80 SUs listed, as well as numerous Ellis mountain SU motors. RedArrow Hobbies is another one you might want to try.