Hi Jim
Welcome to SM.
Biturbos of all types are quite rare in the UK these days as their relatively low values and tendency for rust has meant that many have been broken up for spares. By the time the 222E was introduced, Maserati had sorted out many of the problems of the earlier Biturbos and they were actually very good cars although the handling could be quite entertaining in the wet. I can't imagine there are very many 222Es left, possibly less than 20.
Current values are really dependent on condition, a good one would be worth around £5-7k depending on history, mileage etc. I would say that a manual car is probably a little more desirable than an auto and that white is possibly the least desirable colour but really the most important thing with these cars is condition.
Parts supply is generally pretty good, Maserati made a lot of Biturbos so a lot of used parts are available on sites such as Ebay and from suppliers like McGrath Maserati and David Askew who have broken a number of cars. Service items are readily available so you shouldn't have any problems there, MIE in the USA are an excellent source of this kind of stuff at reasonable prices but you can also try Eurospares or various Maserati specialists in the UK such as Autoshield in Manchester, Emblem Sports Cars in Poole, McGrath Maserati in Hertfordshire to name a few.
Hope that answers your questions, feel free to ask if you need any more information, there's plenty of expertise on here.
