Currently the objects loaded by KmlLayer are not accessible
externally, only via the build in click events.
For kml there are two options I know of:
1. use a third party parser (geoxml3 is the only one I know of), that
renders the kml as "normal" maps markers, polylines and polygons and
allows you to access them externally.
2. import the kml into fusion tables, code GViz queries to simulate
the behavior of the fusion tables click events.
(there are probably other ways as well)
-- Larry