Haynes do a book by Ian Fallon called 'Ducati 916' which lists production numbers at the back, although for certain years it lists figures for Europe as a whole, and in later years UK production.
916 sps 1997 Europe 550 916 sps 1998 Europe 408 Foggy rep sps 1998 UK 202 996 sps 1999 UK 40 996 sps 2000 UK 80
And what about the 916 SP (1995) or the SP3 (1996, although I don't know if any of these were brought to these shores) both prior to the SPS series which started around 1997 as stated above.
I believe the reason there appear to be so many more pre-99 was that they were all made in European spec with kmh clocks and then modifed by the importers when they arrived in the UK, so this is a total number off the production line.
After this time they left the factory in UK spec and you can therefore tell how many officially made their way into this country.
There are a couple of books by Ian Falloon that give all the numbers - check out by author on Amazon or something like that - they're a reasonable read.