These are all the new sail patterns coming to AO with the Dark Sea update. Feel free to use the designs however you like, but please give me credit if you do and link the topic if you can. Thanks!
Note: The file names are not accurate to the sail design names in-game.
Trading or turning in sealed chests (including Dark Sea Ones). I Believe sail patterns are guaranteed with every sealed chest. And if you want a specific color, you can also dye your sails with a paintbrush or go to the new dye merchant at certain cities.