If you're still unable to find a supplier, you could always build your own.

I've published the instructions for building this engine from readily available materials with a total cost of about $20 (see picture) and using nothing more than regular handtools (see picture) such as a hacksaw, files, screwdrivers, electric drill, etc.

If you can get thin enough tubing for the tailpipe then it could be used for powering a model.