The Flying Scott guy had them a few weeks ago when I ordered from him. It is the Merc KG one.
Scan down the list of posts. There has been lots of discussion on impellers lately and what to substitute or where to get home crafted ones. The WD and WG models use the same impeller as the K Model Mercury #47-24447 which has been discontinued by the mainstream sources. Sierra 18-45221 is supposed to be the same but you must cut your own notches to match the Mercury style cross pin.