If you don't find one, there are a lot of threads here about making mounts, and putting two LNBs on a Primestar.
Making your own should be about 10 minutes, and $2 at the local hardware store.
My suggestion: if you have an 84E dish, use a conduit strap. You may have to fab up a shim of some kind....OR you can do like I did, drill a hole in the middle of the saddle on the arm,drill a hole in a stainless hose clamp, insert screw (a) through hole (b) in clamp and inset it into hole (c) in the arm. tighten securely. Loosen the hose clamp, put your LNB in, tighten hose clamp. Done.
If you're missing the whole ARM...then we need to go in another direction.
If you want a pic post back and I'll take one for you.