I would contact Silver Spray Sports and Action Watersports in Fenton. Also give Tommy’s of Detroit (formerly Skiers Pier) in Waterford a call. They are the main dealers for Nautique, Mastercraft and Malibu respectively and should be able to give you some indication of what lakes in the area have slalom courses. Not sure if you tried these places already.
I do not know of a recorded list of permitted courses. DNR is the permitting body for slalom courses and don’t seem to track anything once it’s issued. I ran into this when I was trying to revive the course on my lake. DNR basically said “apply for a new permit” which got killed pretty quick.
I know of a few lakes that should still have active courses but don’t know if there are homes/property available. Pine Lake, Loon Lake, and Watkins Lake were still active. Wolverine Lake and Commerce Lake might still have active courses. Further west, Silver Lake, Lake Shannon, Silver Fox Lake and Whitmore Lake have active courses.