Meowy84,
I saw some idle bar plus on the Brodak website
https://brodak.com/engines.html?p=7 Not quite the ones you want (4-C and tuned pipe) but $8-9. I have not bought glow plugs lately, but apparently finding idle bar plugs is like searching for dinosaur bones. Mecoa may end up being your source. Go easy on the nitro and the plugs will last longer. My bigger question is where are you going to find a carburetor to fit a Forster .29?
Good luck.