I don't know of anyone who sells them stock; not even Rudy at D&R Marine. You will probably need to have them custom made. Be prepared for a rude shock when you get price quotes. Maybe prices are down in this economy, but I think you are talking between $1500 and $2000 for the seven or eight cushions. I priced them out at two or three different places for my Oday 23 about ten years ago, and I gagged. When I expressed my shock to one of the vendors, he laughed and said that he gets that a lot from guys with small boats. He said that the labor involved just makes it cost prohibitive in those situations. If you only paid $5000 for your boat, are you really going to spend $2000 for new cushions?
A word of advice: you are likely to get much better prices at a plain old upholsterer than a "marine" store. If they have a pattern (like your existing cushions), anyone can make new cushions. Closed cell foam, open mesh fabric on the bottom for ventilation, zippers so the covers can be removed to clean, and you are good to go. Don't forget to include the backrests in your calculations. You will have to remove them, but you don't want that old pattern to clash with your new cushions.