What model are you specifically looking to buy ? This forum is for the Jaguar XJ saloons built 1968-1986, plus the Daimler equivalents over the same time period, PLUS the Daimler Double-Six, (V12-engined) cars that carried on in production until 1992, at a rate of about 50 a week. The XJ40 series of XJ saloons started in 1986 with Daimler equivalents. These carried on until 1994, with one Ford-initiated update sometime around 1990, I think. Later cars are best, BTW.
Where will you find what you want ? I'm not sure, try an internet search like this: -
Looking to buy a Classic Daimler sovereign made in the year 1991 in United Kingdom? Complete your search today at Car & Classic where you will find the largest and most diverse collection of classics in Europe
I have to say, though, that you're very unlikely to find the exact car you want as most are now baked bean tins