I actually couldn't seem to find any decent bunk mattresses at any of the RV Surplus places in Elkhart back in April. Very little selection.
Fuel is too expensive and time is too precious to make another trip to Elkhart right now.
They have phones and some have websites, doesn't cost much to check it out before dirving all the way there ! Also don't forget to check out the big truck places the mattresses in the sleepers are about the size you were looking for if I remember right ! BK