I got mine on Rock Auto. ACDELCO 3342190 - 12SI. 78 amp, 9:00 clock. Search for a 1985 Buick Rivera 5.0L. ~$55 with a $7 core.
https://www.rockauto.com/en/moreinfo...000317&jsn=256
They have a pigtail also for a couple $.
There are a bunch of threads and sites on how to wire it. I ran the brown wire that went to the regulator to the #1 connection. This is the exciter wire. I ran a ~16 gauge wire from the #2 connection to the junction on the passenger's fender. This is the voltage reference wire. I ran a 8 gauge wire from the lug to the junction on the passenger's fender. This is the main power feed wire.