Check out AutoZone or Bennys or something like that. They have the type you are looking for. I have seen them before. They use them for trunks and roof racks to hold down stuff.
I no I have seen them around, but have not look lately?? But If I see them I will let you no.
This site has one 36 X 48
http://www.cargogear.com/Nets/CargoNets.htm#stretch
I have seen them in Jc Wintney before also
http://www.jcwhitney.com/webapp/wcs/...atalogId=10101
Just type in bungee nets in yahoo search and they have a few different things there. I found a morter cycle net 15" X 15" also?? Not to sure what size you will need
Good luck