We know that 497 2 seater Strads where built with 225 delivered to Europe. Safe to say that the UK, Germany, Italy and France will have received most of these so I reckon you are not far off Ewan. Perhaps 40 or so UK cars? There is the odd anomaly too as my car is fully UK delivered but was actually destined for South Africa as all SA cars come through Maserati UK. It never left our shores though.
There is probably no way to really know the numbers although that advert which suggest 132 could be correct as the number of cars delivered through the UK network. A few will have been exported, a couple wrecked and a couple with collectors unregistered or off the radar. That makes the taxed/sort numbers probably correct or close to it.
To put the low volume into perspective, Porsche built 1270 carrera gts and 918 of the 918 Spyder (!!).