I once knew of a place in the US that did sell them (MVP Volvo) but not anymore due to lack of interest. They didn't sell one. They might still be available in Europe BUT those may also be for a different trans.

Realize that for YOUR trans (FWD, Auto?), what's involved is a trans R&R and split trans case to R&R your current diff SO it will be VERY labor intensive and hardly a DIY job for those w/o alot of actual trans/diff knowledge and experience to do it right. To top it off, few shops will want to do a "custom" job like that being that there's a chance that things may not go smoothly (w/o further hassles). Few shops/techs care to do things like that UNLESS it's a shop that works on hotrods, custom auto installations.

I'd be happy to keep your present setup being that the only time the wheels slip anyway is on initial take-offs from a stop with full throttle (like racing) or on wet, slippery roads.

In my many years of FWD experience, I have yet to drive one FWD car with limited slip.