Hardware is hardware no matter where you get it. For ASAP, you might try a nearby hardware store and get one stainless (or any other kind) of cotter pin and you'll be back in business. If there aren't any, you can probably make a temporary one out of a small nail, paperclip, pen cartridge, bailing wire, speaker wire, fork tine, dental floss, tape or something in your wife's purse -- good luck!
Sorry you had a problem so soon, and I'm sure your dealer can order you a proper replacement part, but this will get you on the water in the mean time. The fish are waiting!