I also have a mtsport and like it plenty. Why not find a suitable piece of hardwood and make you own? It could be done with three blocks of wood glued together with a type II yellow glue (weather resistant glue) or a polyurathane glue. If you have a rasp and some sort of saw to shape and fit it to you riser. YOU CAN DO IT!

If I' m work or hunting, I' m woodworking.