Curling is typically different in that regard I think. Every team I've known personally to go to national or world tournaments were lifelong friends. They grew as a team and there were no "trades" to suit a roster.
Had to look it up (http://www.amazon.com/Hurry-Hard-Russ-Howard-Story/dp/047083...) but in here Russ mentions how he got pulled in by the guys to help advise on shots.
It was an unusual arrangement to say the least. They went through their lawyer, made a list of the top guys in Canada who could help, and Russ was at the top. The lawyer called, and he accepted.