My '98 has 3 point belts, I'm surprised yours doesn't. Are there anchor points for the 3 point belts on the walls on either side of the front seats? If so, a salvage yard could provide the hardware needed to replace the belts.
You could also check with one of these RV salvage yards, sadly I see that the fellow that had religiously updated the list is giving it up. I hope someone else steps up to keep it accurate and updated.
RV Salvage/Surplus Yards (List) Updated 5/2/16 - RV Forums - myRVparks.com