As usual, the information I've found online is incomplete and primarily hearsay, but it appears that this ratio was available on automatic e21s and the e30 m20 320i, neither of which probably ever came with an LSD...? Aardvark has some gear sets in stock. I might buy one for research purposes since they're only $90, but I'm concerned that the flange location/thickness on the carrier may be different to accommodate the larger pinion gear, which is why I'd prefer to purchase a complete diff if such a thing exists.

Apparently there was also a 3.36 ratio that was used in the 2002 turbo. Metric Mechanic also lists a 3.25, but I haven't found any application that used it, so I'm assuming those are both unobtanium, or at least more than I care to spend...