I have not seen ring caps with rails specific to the AI mounts in the past. If Stacey Blankenship (AINA) or one of the AI dealers here on the Hide can't point you in the right direction, you might try one of these accessory rail rings from Victor at TNVC:
Mo_Zam_Beek, call, pm or email me with the specifics of what you are trying to accomplish and I will be glad to assist. There have been some offered, but they are specific as well to applications.