I agree with the others that have said it is easier to source a complete transmission than individual parts. People are still replacing them with newer, synchromesh transmissions so the original 4 speeds are available.
But - you probably don't need more than bearings to get it good unless someone let it fill with water and rust up. If you have a decent bearing supply shop in your area, take any of the old bearings that you don't trust to them, let them measure (or read the old numbers) and get replacements. This worked well for me.
