I use a small, microswitch-activated, foot pedal for games like Forgotten Worlds and Eco Fighters. Push spinners were cool at the time, but IMO a foot pedal switch is a lot more convenient, since you just have to hold it down anyway.
You could also build your spinner close enough to the button array so that you use your palm or thumb to press the buttons while spinning.
If you really need a push/pull spinner, probably ebay or the buy/sell forums here or other arcade-related sites would be your best bet, assuming that you've contacted RandyT at Groovy Game Gear and he isn't planning on making more.
Good luck!