I see on
http://web.archive.org/web/20020402050808/http://volharding.org/en/series/index.htm it says there are 30 vessels in these series. So far I found:
IMO 9127162 - ALTA MAR
IMO 9155951 - GEESTBORG (with enclosed bridge wings)
IMO 9129122 - LEHMANN BELT
IMO 9155872 - LEHMANN BALTIC
IMO 9179311 - LEHMANN BAY
IMO 9155884 - LEHMANN SOUND
IMO 9155963 - LISTER (with enclosed bridge wings)
IMO 9136216 - LISTERVIK (with enclosed bridge wings)
IMO 9136204 - MIRAMAR
IMO 9179361 - NEMUNA
IMO 9190262 - PARAMAR
IMO 9143788 - RISOLUTO
IMO 9167344 - SOLYMAR
IMO 9129134 - THULE
IMO 9115999 - TORNATOR
IMO 9167332 - TRANSMAR
IMO 9167320 - ULTRAMAR
IMO 9155949 - UNIMAR
IMO 9155975 - VISURGIS
^ 19 ships that look like
http://www.shipspotting.com/gallery/photo.php?lid=2053252 and
IMO 9100140 - GEULBORG
IMO 9100152 - GOUWEBORG
IMO 9100138 - NORDIC CHANTAL
IMO 9116010 - NORDIC DIANA
IMO 9116008 - GRIFTBORG
IMO 9163647 - SCHOUWENBANK
IMO 9196175 - SWING
^ 7 ships that look like
http://www.shipspotting.com/gallery/photo.php?lid=2165850 (superstructure is lower on one deck)
Not finding the remaining 4 vessels from the series.