R-16 Replacement Spring

   
Recently bought a small lot of second hand tracks and found the R-16 auto switch non-functional.

Opened it up to find the main switch spring is over stretched.

Anyone know where to find a replacement spring?

I know it's not much to just replace the switch fully but prefer to repair if possible.

This type of spring is called an extension spring. I just had a quick look on ebay for 'miniature extension spring' and there are a great many; I would need to know the length and diameter to be of any more assistance. I could open one up myself, but you have it open already. A rubber / elastic band should do the job for a while.