I have not had to by a new one but most pits use the same or very similiar thermometers. I googled it and there are places that sell the Tel-Tru BBQ Grill/Smoker Themometer that goes up to 500 degrees. Looks like prices run between $30-40. First place I found was Fire Craft Grilling Equipment. Just look for the Grill/Smoker Thermometer.
www.thunderroadsmokehouse.com - Stump's Prince - Peoria Cookers Meat Monster - Lang 36