I've seen mallard secondaries used...the ones with the iridescent blue across them! Sweeeeeeet looking fletching. Waterfowl season is coming up, got any duck hunting guides in the area that might save wings for you?
To help you determine the primaries from secondaries, imagine the wing as your arm. The primaries are out on the "finger" section, secondaries are on the forearm and upper arm. Primaries work better because they are stiffer, but secondaries work fine, too. Just leave a bit more height to the feather when you trim them up.
And don't forget tail feathers, ducks, geese, and other game birds often have good fletching on BOTH sides of the quill.