anyone know of where to get one or have one for sale?

As a long time Four wheeler and Jeeper prior to owning my current Volvo (second vehicle... still have the Jeep) I would recommend 4 Wheel Parts Wholesaler http://www.4wheelparts.com/ or Off Road Wharehouse (can't find a web page, but if you are in CA look for them. Both are VERY reputable companies.

You can also look at manufacturers directly.
true trac
lock rite
ARB http://www.arb.com.au/

check out: http://www.4x4abc.com/
Web site has info on both four wheeling AND mercedes, and might proove to be a great resource.

Happy hunting.

I've heard/read that you can get a LSD for these axles from a 4-Wheel-Drive shop. The following is copied from the FAQ in the features menu at the top of the page.

Carrier Compatibility. [Query] I have been looking for a limited slip differential for my 83 760 GLE. I have been told that this differential is a Dana 30, which is also used on some Jeep models. I have a chance to purchase a limited slip unit that was an OEM for the 200 series. Can anyone confirm (with a great deal of confidence, since I may base my purchase on the advice) that the 200 and 700 series differentials will interchange? [Response: Abe Crombie] On the back side of axle tube on left (driver's ) side is a label covered by undercoat. Clean this off and see if your model is a 1030 or a 1031. Then determine (label in same place on 240's) if the 240 is the same model. IF they are the same model then the carrier will interchange.
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'92 Mercedes 190E (my daily driver), '93 Volvo Turbo Wagon (a family car w/flair), '53 Willys-Overland Pickup (my snow-plow truck/conversation piece)