If you already have an idea in mind that you want to test, try going to a local college or university and talking to professors in that field. If you don't have an idea, you're just asking them to give up a lot of their time and energy for no gain on their part and it's not likely to happen. It takes a ton of time to mentor a student, and they're only expected to mentor students at their own school. You'd have to be extremely talented at something for them to make an exception. Your other option is applying for one of the summer research programs for high school students, like the ones at MIT, NASA, and the NIH. Applications were due a few months ago, but you can start looking into applying for next summer.