Unless you know what you're doing, the only spare parts you need are springs, a hammer nose and rivet. In most cases, you cannot just interchange revolver parts, the need to be fit by an experienced armorer or smith. The parts in the lock system all work with each other thus, they must be fit to interact correctly or to just fit in the frame. When working on a revolver, I had to use parts large enough to fit to other parts. As an example, the hand and the extractor must be fit to each other to properly rotate the cylinder. As this is happening, the cylinder stop must be fit so it doesn't bind when the hand is rotating the cylinder. Side plate screws are Ok but the one holding the yoke in must be fit!
End of story, most parts are not interchangeable unless you just get lucky.