Yes, they make PTO shafts with slip clutches.
You'll find them on most tillers. The one I used bolted up on one side and had a splined quick coupler on the other. You'll have to order a spline/spline set up with quick couplers on both sides most of the time, I know my dealer does not stock them. Last one I got was $255.00, it was HD. I have a custom shaft on order right now, the dealer used Bush Hog part numbers. The usual Italian company's catalogs don't list as many combinations. Bush Hog has a great selection of drive lines you can custom build, I think they use Italian parts.
Beware of the slip clutch size, make sure it will clear the tiller etc. My Agri-Fab tiller has no clearence for a slip clutch unless you put it in the middle of the PTO shaft which wouldn't work on the 32" length I had to work with. Still using shear pins on that one. /forums/images/graemlins/frown.gif