Problem is no one has heard anything from or about AIA for many many moons as far as I know. I have the email address of one of the top guys and haven't had a reply to questions in a couple of years. Unfortunate as I have 3 different and all are good guns and all of mine came with a rail.
I bet you are going to have to measure and then hope someone knowledgeable can help you or get a blank rail and have it drilled to match.