Maybe you could partner with just one small government to start. Of all the municipalities in the world, you'd think at-least one would be open to the idea, even if in tandem.

Maybe it could be started by a person who works (or worked) at the dispatch center, and is also a programmer (there must be at-least one of those in the world too).

The point is that NYC laughing/ignoring/fighting you is not a good enough reason not to start. (and who's to say that NYC would do any of those things, given the current state of affairs)

Test it somewhere with a private sector need for such a service, like Detroit?