The short model of Spec Ops should work... as long as it is a universal sheath, then left/right doesn't matter. Effectively, for blade profile, you are using a left hand sheath. ie. Looking at a fitted SS sheath, it looks "backwards."
Still, a Spec Ops is hardly "slim." Not sure that you'll find "slim" in a universal production sheath without having one made.
I've got a nylon that that originally came with a SJ. Slim and, though a bit long, effectively the right length. Not sure where you could find another though.
Best bet is to look for a sheath made for the SS. Leather? Chuddy Bear, Leatherman, Kenny Rowe, Rainwalker and others. Kydex? Buy Brown, Tom Krein, Okuden, OST, (maybe David E now, though I haven't seen the product firsthand.) Nylon? On Scene Tactical again.
I'm sure there are others missing. I've just listed some of the ones I own. Check the Busse page for their recommended sheath makers for any omissions on my part.