Are there any foreign exchange student programs for home-schoolers?
I answered your question for “Does anyone know of a credible foreign exchange student program?”. Even though you did not choose that one as the best answer, I hope you found it helpful. YFU does routinely take home schooled students. Some host countries require a little extra paperwork (such as an evaluation by a non-parent), but they haven’t had any significant problems with it. You can see my other answer for more details about YFU. Good luck!