There's no easier way.   Outside of super busy times like spring break and Christmas, it sometimes works to try a date range beginning on Sunday and ending Friday.   Weekends are nearly always sold out these days.  To book full weeks you forget have to book a year out or snag a cancellation.  
I'd also recommend using a travel agent that specializes in Disney.  Even better if you use one that specializes in Fort Wilderness reservations as they know the tricks of the trade.   I use one and it doesn't cost you anything.   You can probably Google to find one if you want to try that route.