Cannonball, here's a potentially useful link:
http://www.lner.info/locos/A/a1a3a10.shtml
I don't know how familiar with british steam, but here's a little overview:
The British had four major railroads:
London Northeastern Railway (LNER) (the railway that had the A1s, A2s, A3s, & A4s)
Great Western Railway (GWR)
Southern Railway
London, Midlands, Scotland (LMS)
If I recall correctly, the labor party issued an Iraq study group/Baker commision style report in 1944 that called for many socialist reforms...including the nationalization of the Railways which I believe occured in 1946. The new national railway was British Rail. British Rail was sold off piecemeal in the late 1990s.
Most of the British steam that survives was actually sitting on scrap lines...many of which was located in Wales. British rail enthusiasts then bought up most of the surviving engines (400 or so).
There were a number of Gresley pacifics that survived...2-3(?) A-2s, 1 A-3 (the flying Scotsman), and 6 A-4s...but no A-1s. There are several famous A-4s that survive...The Mallard...the Dwight D. Eisenhower (in Green Bay, Wisconsin)...the Dominion of Canada (somewhere up in Canada)...the Sir Nigel Gresley. In order to fix the lack of A-1s, a group of steam enthusiasts have been building a new A-1 for a number of years...
http://www.a1steam.com/
You can also find some British railway and model railway magazines at really good magazine stands...I frequently purchase Heritage Railway for my dad at Fountain Square News here in Cincinnati.
Two useful modeller sites for detail parts/wagons & carriages:
http://www.justliketherealthing.co.uk/
http://www.strictline.com/
There are actually quite a few A3 models out there, just not in O-27. Good luck!