Spokesman NickRichards blames the slow growth on a cut in low-profit sales to fleet buyers such as rental car companies as GM tries to boost the brand's resale values.
Delon Armitage, Nick Kennedy and Peter Richards were the other London Irish players named in the elite squad in July 2008 and for the autumn internationals.
Richards, along with former England skipper Martin Johnson, New Zealander Warren Gatland and South African Nick Mallett, have all been linked with the role following Robinson's departure on Wednesday.