You can find a lot of stuff for them on Beachwood Canvas
Or, you can order any early (55-75) CJ spring pack for them. They use the same 1 3/4 width springs as the early CJs. My suggestion is to use the 13 leaf Military spring pack. These can be bought as NOS (New Old Stock) from a lot of the military surplus places. They will still only be 1/4-1/2 ton like the trailer, but will have some extra flex for you, and some extra height. DON'T put lift shackles on the trailer.
If you don't have the space to stow it, let Paul or I know. My dad has one of these trailers, and I would love to have one for myself.
Erik