Finding a high school on a road trip may be difficult. It may be a better idea to do some planning ahead and then visit selected schools. I'd recommend visiting the websites of some organizations that specialize in international student exchanges, like Council. Keep in mind that the school you end up attending will face some bureaucratic burdens (visa and reporting requirements), so it's a good idea to use a school that has some experience with these things. You (and your parents, I assume) will also want a good host family and a responsible sponsoring organization.

Also, as posters have pointed out above, keep in mind that travelling to (and in) the US can be a bit difficult if you're under 18 and travelling without your parents. But your general goal, spending a year abroad, is certainly a good idea and deserves a ^ .