VP charges stoopid $$s for impellers (and everything else too). The MD2020 pump
body is a Johnson pump
with a VP specific mount flange, but the impellers are nothing special. Below is what I have in my notes. Different VP part number than you show, but they do change the numbers sometimes.
Johnson 09-1026B or Jabsco
IIRC, Ive ordered them off Amazon in the past. You can buy a few spares for what VP charges.