have you tryed a gear puller?
also how hard did you hit the sprocket? maybe it needs the persuasion of a 20lb sludge
and you may wanna try cutting down the middle of the sprocket(like your trying the see the cross section) and stooping Cloe to the shaft, then take a wedge or crowbar and wedge it in and split it, but cut it on both sides first so one can break and the other can hinge.