I recently had to do the same thing except for a Nitro. Went several places, but no one carries bunks longer than 5 or 6 feet. Everywhere we went, we were told to make them ourselves.
They turned out to be pretty simple to make. About a 10' piece of treated 2x4, some marine carpet/badding from BassPro, a bit of marine glue, some stainless staples, and lag bolts because we lost some of ours.