Don't know if this is general knowledge but I just received this from K&N filters:

Had the pleasure of meeting you at the recent Hot Rod and Restoration Show. You had asked me about a replacement filter for the RX-8 and I wasn't sure if we had one yet. Well, we do and its part number is 33-2284. We also have a killer intake kit for it. You can view them at our website at www.knfilters.com. Use the vehicle product search. If you have any questions, please let me know.

Best Regards,
Brett Kinsfather