You have a sample? A seamstress should be able to make one. I wonder if the factory would have them ready to go.
There are tons of bedding companies that make yacht bedding. If you currently have sheets that a seamstress can copy it should be no big deal. I highly doubt you'll be able to get them in this manner or from the factory given it's a 13 year old boat.
Use the old bedding for patterns. Buy new regular household sheets and give to a good marine canvas guy. You will have custom bedding for about 25% of the price of yacht bedding companies.
I use regular queen size sheets...not the extra deep pocket fit.. then sew a large flat elastic band around the entire bottom sheet to give a tight flexible fit of the bottom sheet. Works like a charm.