deffinatly craigslist any town that is near you. i love buying and selling on craigslist. also, spend a few minutes googling "fish house" classifides and simalr searches.
also, MNOutdoorsman.com usually has some houses for sale in the classifide section.
good luck. but i learned that buildingyour own is much more rewarding and usually you have a house that is better suited for you......unless you are going to spend a ton of money and go all out..... in that case buy one and then post pics