I have to agree with those who are citing conditions... some of that 80%-frozen slush is very slippery.. even on foot you have trouble staying up right. The only thing that helps with this is a wider tire and better bike geometry. I usually just deal when it comes to the slush... it's not a huge issue as i can generally keep moving and this winter while being colder has produced nowhere near the snow as the last two(not even close!) which required larger tires on a few occasions.

If OP can't find a satisfactory tire, why not purchase the largest aggressive knobby mtb tire he can find for cheap and stud it lightly himself... if you only use it 5-10 times a year for those large storms it should last a while and not cost you a lot of dough.