Go visit you local hardware store or look through the phone book for a place that sells springs locally....it shouldn't be too hard to get something that will do the job. You might even find if you go to a car wrecking yard you'll get something suitable there
**Just "don't" think about buying a genuine cessna bit - don't know if you can still get them or not, but I would imagine the cost of it might be a bit scarey
Cheers