According to the NHRA rule book, the "crotch strap" or submarine belt, can pass in front of a stock seat but the tie down point must be behind the chest line. On a "Y" type belt it can be rolled around the cross bar behind the seat but it must have a "U" shaped bracket welded on the bar to keep the belt from sliding side to side.
www.summitracing.com is your best source and cheapest. Their catalog has a greater selection than their website, so just order a catalog. RJS, RCI, Stroud..lots of manufacturers. One thing to ask, if the belt can be re-certified, otherwise you will have to buy a new one every 2 years. Stroud does theirs for $35.00 + shipping.