My first thought would be to go to Searay.com and go to the archives and pull op the owners manual for your year/model. They should have a part number accompany it. The you may be able to order from Sea Ray.
My second thought, (i like this one better

) is to buy some starboard and make a 2 piece section then have an upholstry shop make a cushion for it.
I have the filler cusion for our 2005 and it is really simple. I can show you pisc if needed.
Good Luck