[eluser]kanjimaster[/eluser]
I don't have any hard research to back this up, so it's just a personal opinion ... but HMVC isn't a big step up for even a modestly talented developer, so I'm really surprised that requiring it has a significant impact on pool of developers available to you.
But that's your experience so let's go with it. The developers that you're losing while requiring HMVC are going to be those who either don't understand the benefits of proper modularity, or don't value them.
You clearly understand, value and benefit from HMVC. Therefore it would not only be a big backward step to give it up, you'd also be opening up your jobs to less able developers and the frustration that would come from reducing the re-usability (and potentially quality) of the work that they produce for you.
I suspect that what you're really seeing here isn't a lack of HMVC skills, its that really good developers, who share your philosophy and experiences, don't have problems finding work, so don't hang out in the places that you're looking.