Stoped down the Tamron 11-18 Digital lens is ok if not particually fast. Your in a tough situation so some compramise is going to be necessary. I checked their website and it states it suports the Sony/KM mount.
I've linked a brief review over at Nikonians. They looked at 4 super wide zooms (Inc. the Tamron) from a Nikon perspective.http://www.nikonians.org/nikon/nikkor-12-24mm/index.html