Find a soaring club that tows in a Piper Pawnee or a Cessna Agtruck. While they may have high minimums (say, 100 hrs tailwheel time) they often waive them when they're short of towpilots. In my club's case, the "open pilot" clause in the policy required 100 hrs, but for a $100 or so they were able to add me to the policy by name. I had about 90 hrs of tailwheel time, so it was an easy stretch for them.