www.ackits.com. They have everything you need to rebuild the Nippondenso. Also, there's a great Pelican tech article on the rebuild process.
I was told by a leading US distributor of both the Sanden and Nippondenso compressors that the Sanden was not worth the extra bucks. Also, there is a common misconception that the Sanden is a rotary compressor. It is not...it's a five-piston wobble plate compressor. Vertex advertises it as a rotary, and they're just plain wrong. The only rotary compressor, as far as I know, is the Seiko. The place where I bought my front fender condenser/fan assembly thought that the Seikos were junk. They also told me that the Sanden was not appreciably better than the Nipponenso.