Hi,  I suggest Guy Forstrom seeks out a small spring manufacturing
firm and supply them with a sample to copy.  I say 'small' because
it's likely that a large manufacturer would only do a production run,
whereas a small company would have lower tooling up fees.

Failing that, some 16 mm film projectors used spring belts to drive
their spools, maybe Guy could source one of these and put the parts
to good use. (Don't let any projector restorers know what your doing
in case they get hacked off!)

Cheers, Paul Camps