Holland had it on 2 ships last I checked though it's risky to use. You are required to pay book price for a single travelor, then if they find you a match you will be rebooked at current prices.
When I looked: 35 day trip 3400 double price, 6000 single, 8000 through match program. If you do it early I guess you could pay deposit and cancel if they dont find a match.
Best bet is to find a roommate through this site or others. You can book through any travel agent and they will split the cost and send documents to both parties.