there is a very nice ultra wide, made by Tokina, but it isn't available in Kmount. 11-16mm 2.8, a friend of mine has one in nikon mount. an excellent lens.
Tokina I don't know what you consider 'ultra wide' in terms of rectiliner lenses, but I don't think there is a lot of difference between an 11-16 and 12-24. 1mm difference at the widest end of the range. there is of course the sigma 8-16mm. anything wider than this, and id think you'd be in the specialty lens territory. i.e. something that is too expensive to mass manufacture on the same levels as other lenses.