The number of publicly available production quality authoritative dns server software packages is limited. Load balancing and geolocation are not available as standard supported features.
The purpose of authoritative dns servers is to provide answers to dns queries for the specific dns zones for which authority has been delegated to them. In other words, these are the servers which the domain registrant has designated as the source for dns answers specific to that zone.
In that role, it is imperative that the authoritative dns server be reliable and standards compliant.
The list of servers recognised as fulfilling those requirements includes:
The dns servers which contain these features are generally not publicly available. They are the basis of services or products of their respective owners. As such, they are unlikely to become publicly available.