I don't think any third party manufacturer makes weather resistant lenses for any camera.
I'll add to the sentiment that you shouldn't treat the weather-resistance like an all-or-nothing deal. I don't have any WR or DA* lenses, but still appreciate that I can treat my K20d like a normal (old film, reasonably-gasketed) camera, rather than an open circuit board, when it comes to stuff like this.
It's a lot easier to protect just the lens than the whole- rig-from-all angles. And let's face it, weather sealing doesn't make a wet lens element or eyepiece any more fun to deal with.
A fully sealed rig would be on a different level of convenience, but I mostly see the sealed body (Which I'd be hard pressed to want to give up) ...as freedom from obsessive babying of all the electronics.