I was a little short on time for the last reply, but to elaborate a little...
Besides looking around online for a used set, you can check out Sand Tires Unlimited website.
You can also call and talk to Mike at http://www.mkemotorsports.com/
for tires and tire recommendations, as well as Gary at http://powerproracingproducts.com/
Both guys are great to talk to and can give some recommendations. I would highly recommend however, you really take into consideration how much power you have. Putting too much tired under a Jeep is one of the most common mistakes I see people make, and it kills power.