I got mine from http://www.racecaroesupply.com. I found Racecar OE Supply to have the best price on these small alternators. Their website is a bit hard to navigate - from their homepage, go to "alternators", then to "1-WIRE SELF-EXCITING ALTERNATORS", then look at their A800. The web page describes it as a Nippondenso.
I wrote a thread on installing and wiring these alternators a few months back - you might search for it.