I should have said custom or aftermarket parts. At the moment I am having the rifle looked at because it jams way too much when working the lever. I don't need all those parts but I might have to replace the extractor and I figured I might pick up some of the smaller parts to have on hand.
Understanding why your Marlin is jamming may be a quicker solution to the problem rather than just changing some parts out which could be expensive and time consuming. Here is a link to many common and not-so common Marlin lever rifle jams from the Marlin Owner's forums. Parts sources: Mid-Way, Brownell's, Marlin, eBay, Numrich, Wild West for a Happy Trigger and Bear Proof ejector. Good luck!