Ken,

The easiest way to handle this situation is to assign each location a code to id the lcoation, then use the standard way fo generating PKs and prepend the generated PK with the Location Code,

* Location code ABB
lcPk = GetNewPK()
* lcPk = "123456"
lcPK = lcLocationCode + lcPK
* Now lcPK = "ABB123456"

This way even after merging it is easy to report by location if needed. You only care that any given generated PK is unique within that location, not within the entire organization.