I can't really help with the figures for the 4200/Gransport but I do have the production numbers for the 3200. In total 4795 were produced (2689 manuals and 2106 autos) and of these 870 went to the UK. In addition there were 250 Assetto Corsa models built of which 75 went to the UK.
I have a quick search to see if I could find any data for the 4200 and Gransport but all I could find was the overall production numbers for the Maserati brand by year for worldwide production:
2009: 4,489 units
2008: 8,586 units
2007: 7,496 units (5,455 Quattroporte, 1,779 GranTurismo)
2006: 5,734 units
2005: 5,568 units
2004: 4,590 units
2003: 2,839 units
FY2001: 1,869 units
FY2000: 2,027 units
1999: 1,538 units
1998: 620 units