Start here if you haven't already: http://www.steamboat.com/steamboat-life/employment/employment.aspx
They are probably more focused on winter 2013-2014 right now. Not sure when they would start posting jobs for next summer.
I'd also look into the Steamboat Bike Shop located at the base area. It's a cool little mountain bike rental/retail shop, you'll learn a ton, and get to mountain bike a lot (if that's your thing).
They'll probably have a listing in the same link that jg atl posted, most likely sometime around the end of April/beginning of May.