When you purchased Premiere Elements 9 did you purchase it as a download to your Windows computer or did you purchase the box packaged version that comes with installation disc for Windows and Mac? If the latter, just use the Mac installation disc for your new mac computer.
If you purchased a download to your Windows computer, then you have Premiere Elements 9 Windows installation files that cannot be used on Mac computer. Consequently, if you want Premiere Elements 9 installed on your Mac computer, you will need to find a vendor that still has Premiere Elements 9 Mac in stock and use that for your new Mac computer.
Please let me know if you are OK with the above. Any questions or need clarification, please do not hesitate to ask.