Jim,
My single extension 8x15 was ordered with two extra plate holders. Apparantely, they are difficult to obtain, even for the seller in India, John Alex. One has a partial light trap on the end of the slide that needs some fixing; the other side is fine. Since I have two others that are working, why bother with more work? You can buy it from me or try your luck with John. jn(dot)alex(at)gmaildotcom, me: michaelatstudiocarterdotcom