NO LBC - trailer 5' x 8' decking?

All,

I'm in the middle of rebuilding a trailer this weekend that had a rotted 
out floor.  It just hit me yesterday that the old floor was two pieces 
of plywood; four foot and eight foot in length.  However, the pieces 
were five feet wide instead of the standard four feet.

Does anyone on the list know how to order / where to buy such a weird 
piece of lumber?  Maybe it's standard for decking or something...

 - K