Mealworms, bean weevils, and fruit flies are easy to culture, so once you get your hands on some you should be able to produce your own. With winter coming, field collecting of insects will be difficult at best.
My best advise is to bite the bullet and order what you need on-line. For fruit fly cultures, medium, and other supplies Black Jungle and Josh's Frogs are great places to start. I especially like Josh's fruit fly medium. I also find Drosophila hydei to be the tougher, hardier fruit fly.