If anyone is still having problems finding Centennial, Bells (www.bellsbeer.com) has it both in 1lb and 1 oz bags. The price seems pretty reasonable. I didn't even know they sold ingredients until now. I look forward to trying this recipe.
I can personally vouch for Royal Oak Brewery(a very fun little town, tons of bars and food), The Great Baraboo(sic?) (they have fantastic food), and Dragonmead (really good beer). I'd love to visit all of them again sometime. Enjoy!
I just ordered this from Lowes: http://www.lowes.com/ProductDisplay?langId=-1&storeId=10151&productId=1079173&catalogId=10051
It's free delivery. The only downside is it won't be here until late next week.