Yes but guessing not so much in WY. If you live near parts of the country that have a strong wooden boatbuilding tradition you can. You can order plywood up to 32' long from Boulter Plywood last time I checked, it's just 8' plywood that comes prescarfed together.
Not 5'x10' but you can get 4'x10' MDO which is an exterior grade plywood faced with a resin impregnated paper on one or both sides from luber yards or sign shops (it's used for signs a lot).