A local botanic garden uses big pumpkins for decoration and display in the fall. I think they are grown under contract by a local grower. I am pretty sure they pay top dollar for a few big ones. They are about 4 feet in diameter--amazing. They also buy a lot of medium size for decoration 12 to 18".
If you can find a farmer's market to sell them or a local store--should work. Its a lot of work to load and unload them.