Miracle's web site can be iffy. I couldn't get an answer about a custom size. Went to a Quilt Show and there was a rep there. She had the total list, and my ironing board was actually on it! I told her the web site was off. Maybe if you can find a list of distibutors for Miracle, you might get faster service.
I've ordered two covers from Miracle, both at shows. One rep was Calif. based. Both of the reps had my cover to me before the promised time.
I have an old Pfaff board. It has a fan and motor that draw steam through. The Miracle cover is the closest in fabric and underlying liner to the old blue cover I got with the Pfaff board.