You can find folks who sell Hedge Apples, the seed of Osage Orange trees. They make many claims about them, like they keep bugs out of your basement!
Sometimes you can find really creative folks selling just the seeds, 25 for a dollar. There are about a kazillion seeds in a hedge apple, and a kazillion hedge apple on a tree, so if one can find the buyers you could do well.
They're easy to mail, just put them in a envelope. For the apple, if it's green it's about a hard as a softball, and the same size. No special wrapping needed. Just put it in a box, oh one might wrap it in special paper to indicate it's precious value to the buyer!