I've looked everywhere and had no luck at all. I put a VDO Dayton MS5000 in my wife's car - superb unit, and the maps are £80 (not £200 like the Lexus ones).
Having said that, Lexus run a very good free loan service when you're going abroad (although the maps are a little out of date). On the map of France I borrowed last year, none of the motorways around Calais were in it.