It was a two-person freeware effort so, understandably, that can be hard to sustain. And of course around the same time it stopped, Command: Modern Air and Naval Operations took off as a successful commercial project, and much of the Harpoon-related community followed - and arguably, that community isn't quite big enough to sustain interest in two similarly-featured games, especially when one has a business model and the other has only the developers' own enthusiasm to run on.
I don't have an installer on hand either unfortunately
A bit of searching resulted in some hits on third-party sites that have it, but I can't vouch for how safe and reliable they may be.