You're going to have trouble finding true non-DOT knobbies in sizes that'll properly fit your Uly.
Pirelli Scorpions come in 17" but I don't believe you'll find them in the right widths. Even if you could, you say you ride 90% on slab? Knobbies would be a total waste. They'll be sqirelly, loud, & you'll be lucky to get 500 miles out of them.
You'll be better off shopping for a set of 50/50 70/30 or 80/20 dual-sport tires.