Welcome to the new Wizard Outboard Forum.
Try Ferguson Poole for a Wizard impeller http://www.fergusonpoolemarine.com/enginecoolingsystem.html
I just wanted to bring this forward for the new guys on the forum.
I found this today. Lot's of good information: http://johnsoldmercurysite.com/whitepapers/manuals/MARK%206.pdf