I have and use a number of lapping (flattening) stones to keep stones flat. They include Norton stones, DMT stones, and metal plates that are crosshatched and are used by tool and die makers with something called Clover compound. Clover is an oil based abrasive available in a number of grits. The Belgian stones I keep flat on DMT Coarse stones of the continuous diamond variety. When you say a "barber's hone", I don't know exactly what you're referring to but they are often belgian yellow coticule stones. The synthetic razor honing stones you can buy used and cheaply everywhere can be flattened on DMT stones and probably on Norton lapping (flattening) stones to positive result.

Howard