Looks like someone made that impeller. It is basically the same shape as an original. Occasionally the rebuild kits with new shaft and impeller show up on eBay or other sites. Might try Marx Parts (
https://marxparts.com/) (7323 CTH-N, Arpin, WI 54410 Phone: 715 652 2405) or Gary Wallace (
http://earlychevyparts.com/) (600 Susan Road St. Louis, Missouri 63129 (314) 293-1991). They have parts that the Filling Station does not stock.
Caution: The later pumps have an impeller that looks the same but is thicker so won't fit into the space available. The closer the impeller fits the better it moves coolant.