I found boards at a specialty store that were longer than the 18 foot hull I built, probably around 20 or 21 foot planks. Ripped them and milled them myself. I would consider in your position, to make up some sort of design on the ends using the different colours you have available and use that to hide the but joints. You can cut them on angles so they look like scarphs and make different designs. It'll look way cool and you'll be able to say "Yeah, I did that!".