I can't speak about your clinical to I/O change over, but if you want information about I/O programs, there is an abundance of information on SIOP's website (Society for Industrial/Organizational Psychology.)
http://www.siop.org/gtp/Default.aspx
I would definitely start looking there. I don't think you really have to have a business background per se - but your research interests should be narrowed down, and fit like a glove with the person you hope to work with at a certain school. Having research is a definite bonus, even if it's not in the area of I/O. When I applied to social/personality programs, the fact that I'm doing a Master's thesis (even if it's in an area unrelated to the program I applied to) was a huge plus. If you can talk about your research and demonstrate you know experimental stuff, etc - you will be OK. They can always teach you the specifics of I/O, but the desire to research and what have you, comes from within!