http://www.arubanetworks.com/assets/og/OG_AP-210Series.pdf
As you found, AP-220-MNT-C2 is for Silhouette and Interlude rails that will support the 215, as well as the 225, 205, and 300 series. The APs themselves include a mount for the 9/16" and 15/16" rails (AP-220-MNT-C1). If there is something special (a non-Silhouette/non-Interlude recessed 15/16" rail), then we don't have a default mount for it and something would have to be customized, or you could look at mounts that cut into the ceiling tile itself (the AP-220-MNT-T for example).