Small cam, especially the NHH small cam parts can be difficult to source.
Cummins is still your best shot at finding the correct parts.
Unfortunately for the owners of Crowns and Gilligs with small cam Cummins, some of the NHH specific parts are approaching unicorn status. Even finding people who know anything about them is getting difficult to find.
For instance, the PT fuel pump on an NHH engine is exactly like every other Cummins PT fuel pump except for the fact it is mounted on the front side of the front cover instead of the back side and turns opposite of every other PT fuel pump. Which means the NHH front cover is unique to the NHH and therefore harder to find replacements if your should get cracked or broken.
You may have to find a water pump rebuilder or machine shop who can make up a new shaft and bearing. That is if the impeller is still in usable shape.