1. New methods: Location\Handler::findLocations( $locationCriterion, $offset, $limit ) and
Location\Handler::getLocationCount( $locationCriterion)
2. Reimplement LocationService::getLocationChildren, LocationService::getLocationChildCount by using these methods

The $criterion is restricted to AND, OR, NOT and basic filters which are used in Permission Checking (subtree, section, contenttype, ...). No Fulltextsearch, FieldSearch allowed.