for wool tights try Ibex, VR. They make THICK wool, tights, non chamois ones. also, try Elliot Bay Cycles if you want to shop local, they used to stock good wool tights.
Boy, super cold tights would be the kind for xc skiing or ski mountaineering.... there's got to be some hella warm Schoeller WB400 tights out there...I have a set of The North Face bibs, super stretchy Schoeller WB 400, total wind and water proof, and thick fleece on the inside, super stretchy, but expensive!
The company called "Beyond Fleece"
custom makes to order winter workout clothing out of WB400, maybe they could whip you up a nice set of bibs!
www.beyondfleece.com