There is only a sore loser. A sore winner would be a winner who is not happy due to one reason or other, which generally does not happen eg. not happy with the prize money or benefits which the organisers overpromised and under delivered.š
Winners are normally either humble or arrogant and boastful. But generally most are overwhelmed and happy so they do not complain.š
Summer3, that is semantics. Sore winner is a term used to describe people who do not show grace and dignity in winning. It can apply to the winner or to the people who support him.