Prestone makes a Deicer Windshield Washer Fluid. Rain-X (or one of the other windshield treatments that) also makes washer fluids under its brand has a special deicer formula also. I've used both with great success.
Keep in mind that products like this tend to be regional. If you're traveling and run into such weather, needing some, head for a local supply house and you can usually find it -- unless the locals have already bought the supply up.
1997 FZJ80 The Sacred Cow 152k, 255/85 R16 BFG KM2 on 16x8 Toyota Steels Rims, ARB w/ XRC12, dual batteries/Hellroaring isolator w/ Blue Sea battery switch feeding winch and dual inverters, CDL switch w/ 7-pin mod, cupholders!, 8-ton pintle hitch w/ GI chain plate, blue-PHH, working power antenna, FSM, camper conversion
M101 CDN Tagalong to the boonies, 255/85 BFG KM2 on 16x8 Alloys, w/ custom extra wide fenders, fresh OD paint, bungied tarp and bows