I'd just search for the size you are looking for directly (google, ebay, etc.). Most filter dealers/manufacturers won't have GPs listed unless they make a specific system for it. I too recommend AEM Dryflow. It depends on what setup you are using for what you will need. Figure out the diameter intake you will have and mounting location and pick a size (ie. I use a 4" x 9" filter with my FWI). I believe the majority of AEM's cones are 5" or 9".