TPMS sensors as fitted to the 2005-10 QP V, GranSport & GT (see full list below).
This is the OEM sensor but without the Maserati/Ferrari branding. I bought one last year and fitted to my 07 QP Sport GT with no issues whatsoever, after a careless tyre fitter broke one. Absolutely not an aftermarket item/fake/copy and 100% compatible with the car. Each one comes with a new valve and seals, so no need to buy the valve service kit (the alloywheelsdirect photo doesn't show the valve).
Huf Beru RDE001
Buy with confidence from this German supplier - very helpful customer service :
http://www.alloywheelsdirect.net/
http://www.alloywheelsdirect.net/tpms/huf_beru_tpms_sensors
At the time of writing they are £67.20 each plus £10 delivery inc VAT, so just over £280 delivered for 4.
Compatibility list from US vendor TPMS Direct:
From
http://www.tpmsdirect.com/Huf_Beru_RDE001_TPMS_Sensor_p/rde001.htm
2010 GranTurismo
2010 GranTurismo S Automatic
2010 Quattroporte
2010 Quattroporte Executive GT
2010 Quattroporte S
2010 Quattroporte Sport GT S
2009 GranTurismo
2009 GranTurismo S
2009 Quattroporte
2009 Quattroporte Executive GT
2009 Quattroporte S
2009 Quattroporte Sport GT S
2008 GranTurismo
2008 GranTurismo S
2008 Quattroporte
2008 Quattroporte Executive GT
2008 Quattroporte Sport GT
2008 Quattroporte Sport GT S
2007 Quattroporte
2007 Quattroporte Executive GT
2007 Quattroporte Sport GT
2006 Quattroporte
2005 GranSport
2005 GranSport Spyder
2005 Quattroporte
NB It doesn't matter if you move the sensors to a different corner because each wheel arch has its own aerial to tell the car which sensor it's talking to. So you just have the new sensor fitted and press the button to calibrate, as in the manual.