I don't know if there's ever been a Showcase Thread for Greg's 12-string, or the 6-string either. Just remember that they were mentioned. The 6-string was a '75 medium-scale, with zebrawood top and cherry core.
As far as I've ever read, Alembic never kept track of how many of any model was produced. I can't imagine there would be a huge number of 12-string guitars, but they had their time. Maybe Mica would make a guesstimate at the number.