Aaron,
When the U.S. auto makers were putting in alternators that were made in the USA, e.g. Motorola, Delco, ForMoCo, parts were easy to get.
If you look at the kits available they are for the alternators made in the USA.
Getting parts for the Nipondenso alternator is a problem because the make considers all the parts to be "proprietary". The parts are overpriced because of a thing called "transfer pricing" (which is a discussion for a whole other forum).
Find a local shop that can get parts for your alternator. Then find out how much it will cost to get your alternator rebuilt will new diodes, brushes, and front and rear bearings. They should also clean up your case and test all the other components.
If you could get a rebuild kit it may not help you. The diodes are soldered in place, and if it is not done properly you could ruin the new diodes.
If you can get it rebuilt at a reasonable price, this is the way to go. Do not be surprised if the rebuild shops tell you that they cannot get the parts, or if they do get the parts they will be very expensive.
It may be as much to have your alternator rebuilt as it would cost to buy a rebuilt alternator and turn your's in as a "core".
Check it out, and let us know how you do. rangerj