The teacher or principal probably knows a lot about the parents of the students, and may know which ones have vacant land. If the school is willing to act as an intermediary, you could have your next flying field very soon. This may be something as simple as showing up at a pancake breakfast, or something more elaborate. If you've exhausted those resources, your next step may be to find a piece of land on your own and track down its owner. Before you start driving around, get on your computer and download some aerial photographs of your local county.
Vacant fields show up real easy on aerial or satellite photos.
Print these photos out, so you have a hardcopy. I'm sure you'll be able to quickly find a field that might make a good launch range. Next, you'll need to track down the owner of the land. This will involve going down to the county clerk's office at City Hall. Show him the aerial photos, and compare them to the County Clerk's maps.