ok anorak back on....
the P4 was introduced in around 1990 in the UK, earliest ones were on an H plate, the model didn't get any updates for the UK market and was discontinued here in late 1992 so the last UK cars would be on a K plate.
The model continued in Europe until the end of 33 production in 1994, cars after late 1992 were badged as Q4 and had the same updates as the later 2wd versions sold in the UK eg catalytic convertors, and later style 16v wheels. Most European versions also had abs which was not available in the UK (the abs componentry was fitted where the battery would go on a RHD car and Alfa Romeo didn't bother to engineer it for RHD markets. Interiors were slightly different to UK P4s, Recaro seats were an option and were the same half leather/alcantara versions that the last UK 16v cars were fitted with. Standard seats were similar to those fitted to the European Imola model (half leather/alcantara but not Recaros). Most European versions did not have a sunroof as fitted to UK cars and many did not have headlamp washers or front fog lights.
Also available in Europe were permanent 4 wheel drive versions of the lesser models e.g. 1.3/1.4/17IE including sportwagons.
The last versions of the 33 had much better rust protection that the earlier ones, they were fully galvanised but that doesn't mean they're immune to rust, just less rusty than earlier cars.
A/C on UK cars is very rare, I would imagine only around 15-20 cars were fitted with it, I've only ever come across about 4 of them.
I would say if you really wanted a 4wd car you'd be better off with a Q4 from Europe, they'll be higher spec, later version so less likely to rust and probably easier to find, assuming you don't mind LHD. Although advertised as a P4 this one is actually a Q4
http://www.autoscout24.it/Details.aspx?id=214441105
As for finding one in the UK, it won't be easy, unfortunately 33s reached banger money a while ago so lots have been scrapped or abused, values are creeping up again now and there are a few out there that have had money spent on them. There was a track prepped P4 on ebay a while back but I think it sold a while ago.
The supercharger option is do able but there's nothing available off the shelf so you'd have to develop it all yourself. With bigger pistons, cams , adjustable pulleys, a decent exhaust and a custom ECU you can get around 200bhp. I guess that lot would be around £2.5k. If you want to go to 2 litres you're looking at about £5k plus and potential for about 250bhp.
Unfortunately H815BFM is no more, last taxed in 1999
Anorak off, I'm a bit of a saddo aren't I?
