where to find 8.75 sure grip units used

The new ones are better off avoided. Mopar shipped a ton of units with bad heat treat on the side/spider gears. I got one, and it lasted all of 8 passes, after a cone unit had held the same car for two years. This is the reason these are very hard to find right now, and Mopar hasn't shipped any for a long while.

There are a couple of vendors that sell replacement internal gears with the correct hardness, but who's to say the "new" one you're buying has the good gears or not? And if it doesn't the damn gears cost almost as much as a vintage clutch sure grip.

I ordered a set of the "good gears" for mine, and they seemed to work ok, but I got tired of worrying about it and put a detroit locker in the car.

I have the clutch sure grip hog-head sitting on the shelf. Id say its a back up, but I am not real worried about breaking the locker.