A good source is Vacations To Go website. There are cruises on some foreign lines like Pullmantur who ply the Caribbean without going to US. You can pretty much make any port your start/stop point. Have no idea how a Pullmantur would be. I've always said if its clean and the food edible I can enjoy the blue ocean and the ports. If the food is above that, great bonus. You can also search for cruises originating/ending in Cozumel and comes up ZILCH.