There's a couple of threads on here that talk about using a J72 as a base for the E class, I can link some later if needs be.
The new Hornby pre-grouping and Hattons Genesis coaches (whenever the latter finally release, that is) would do for coaching stock if repainted into the appropriate livery.
In theory, a Bachmann N class would also work to represent the almost completely identical K1 class, though these were only used on the Midland in the very last year-ish of it's existence, which makes it's use on such a layout quite limited.
Now, I'm going to be shot for what I'm about to say, but a Fowler 2p or a Tri-ang L1 could maybe make for a very, very, very, rough representation of an A class 4-4-0 (the L1 would probably work very slightly better, since the rear splashers are less wrong and it has almost the right windows).
This thread might also help, though it is in EM/21mm, which is close enough to OO: