Crotch strap for ASW 15?

My current harness is a Schroth equipped for a fifth strap. However, my understanding is that they supply only manufacturers now, not re-sellers. Will the tab on other belts fit a Schroth buckle? I barely fit into my cockpit lengthwise. I completely remove the adjustable seatback so my head won't hit the canopy. This results in a slightly more reclined (and very comfortable)seating position making it easier for the lap belt to ride up. The ASW 15's cockpit doesn't have anything that forces you to bend your knees or stop you from "submarining" in the event of a sudden stop. I'm concerned about being legal but more concerned with being safe I've read more than one account (like the one above) where pilots credit the fifth strap with saving their lives or preventing serious injury.

Mike

mdfaddenatgmaildotcom