If you have no metallic (conductive) paths between the location where the main service is and the Building with the 200 amp panels, then you could do as described in NEC article 250-32 ('99 NEC), or 250-24 ('96 NEC).
By this I mean "Re-Ground The Noodle" (bond the Grounded Conductor to another local GES).
If the feeder from the 600 amp service comes up into a distribution panel, then bond the Grounded Conductor to the GES + equipment at that panel.
If distribution is done via a common gutter, then POSSIBLY could bond the GES to enclosure + Grounded Conductor in the gutter.
This should be verified OK by the AHJ first.
I would think that bonding each 200 amp panel's Grounded Conductor + enclosure to the GES would be OK (verify first!), but it seems like more work than needed.
My choice would be to go with a single bonding point, sized per 250-66 ('99 NEC) connected to a compliant GES (Grounding Electrode System) which is "Local" to these panels.
Other method would be, of course, to add an EGC (Equipment Grounding Conductor) with the feeders.
If I find some additional data, it will be added.
Working on some system grounding schematics, and hope to post them soon.
Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!