I found some water pump kits for 6 and 9 horse commercial motors which are shown on another site to also fit the 14 horse Workhorse/Worktwin motors. Nothing mentioned about the 12 horse. Part numbers for the kit are 391389 and 389796. Photos show the same 389732 housing and the liner is 324097, impeller 389623, wear plate 323597, pump housing gasket 324901, grommet 302497, screws 324982, washers 324956, and drive pin 300611.
I’m thinking 389623 might be a good part number for the impeller you need.
https://www.amazon.com/IMPELLER-0389623-JOHNSON-EVINRUDE-Outboard/dp/B071D5CPJ2
