I have a 3.25 LSD for you - recently pulled out of an '85 E24, 240k km, turns well, light surface rust only. You'd have to swap the output flanges and rear cover to E30 ones, but otherwise bolts right up. I want $300 for it, the catch is I'm in Calgary, so shipping cost would be extra, and these diffs are heavy!
I have an S52 E30 as well and am running a ZF with '98 E36 M3 manual driveshaft, with E30 CSB mounted backwards, and E36 M3 guibo. Theres a lot of debate about which way to mount the CSB - forwards/backwards as it affects the drveshaft angle, some guys have worn out their CSB really fast, but mine so far is fine. Stay away from the E36 DS from auto cars or the ones with CV style universal joints in the rear as the consensus is they won't work with your set-up. You want the '98-'99 manual M3/328i driveshaft. Also make sure to use new nuts for the guibo and rear diff flange to DS as they're one time use, and bad things happen if they loosen off.
Let me know if you want the diff.