Check out Johnstone Supply.
They will sell parts to "Non Certified" A/C service personnel. Some of the other supply houses will not sell to you if you are not licensed. Kind of BS but whatever.
Replace the contactor, when you filed the contacts you most likely removed some of the coating on the contactor. If the fan turns freely I would leave it alone for now. While you are in there, clean the coils with 409 or buy some coil cleaner at the supply house. Spray them good and rinse well after about 15 minutes. Cut the power to the unit before cleaning. Also turn off power to the furnace and outside A/C unit before replacing contactor. the "pick" for the contactor comes from the furnace. You don't want to blow a fuse that feeds the 24V.