Mac App enterprise distribution outside AppStore with MapKit
Ideally, Apple would offer a Mac equivalent to the iOS Developer Enterprise Program. Sadly, this is not currently offered.

Contact Apple

Contact Apple through Developer Technical Support or through the Mac App Store. They should be able to suggest the best approach – which Apple will support. At the very least, it will help prove demand for the capability.

Ad Hoc Distribution

Depending on your situation, you may be able to use ad hoc distribution. It is designed for testing and imposes limits on the number of computers involved.