You would have to go to Mangsun (sp) for replacement parts. I don't know if they will even sell you them, but you can ask.
As far as spring vs no spring.
It won't add any performance, it can't. As stated before as soon as the slack is out it is a solid coupling. It actually takes about 10-15 deg of rotation before it is locked up. That being said that would be degrees in relation to the supercharger. Since the supercharger is spun at 2.7:1 then in crankshaft degrees that would be significantly less, so you see that it really makes no difference because you aren't losing any pumping cycles and the amount of air moved in the same time period is the same.
The problem with the spring couplers is that they break. I can't tell you how many superchargers I saw on Ebay with " customer said it was noisy, so it was replaced under warranty" or " it made noise and was replaced under warranty. A supercharger is supposed to make noise!"
Every supercharger that had that description I am sure had the same problem, a broken spring in the coupler. Every thing from M112's for Lightning’s M112's for Jag's M90's for the BOP crowed. I bought a M112 off of a Jag on Ebay and knew that was the problem. But hey, for $125 who's bitching?
Jeff