Does crossman make 20 cal pellets?

Actually YES they do but you won't find them under the Crosman name. Years ago Crosman bought out both Benjamin and the Sheridan air gun companies. Sheridan uses 20 cal pellets. Crosman makes the pellets but they are under the Benjamin or Sheridan brand name.

20 caliber pellets are not easy to find. You could try Bass pro, Cabelas or Pyramydair on the web.