That attitude isn't an impediment to them being a good engineer with a high level of professionalism. If you dont't mind paying their rate, what's the actual problem?

IMHO the engineers that don't have this attitude have a tendency to burn out.

It could be they were burned by a previous employer and are a bit jaded now. If you're fair and open in your dealings with them and share in the success of the company (not that you're not doing these things already) their attitude may change. A lot of "good CEO training" involves learning how to get the most output with the least input when it comes to employees. I think they assume people don't know what they're doing, but it just leads to an adversarial environment.

have you considered following up with some of the good developers that didn't follow through to find out where they ended up? You can probably make a decent rough guess at how much they're making based on who their new employer is/location.

Also hiring is difficult... have you considered hiring a recruiter to help?