Rob,
A great little layout,very impressive.
If you are looking for something smaller in coaches you could try a couple of the Slaters 4 wheel ones. I believe these lasted into the 1950's on workmens trains, which would also fit well into your Welsh colliery scenario. I expect by that time they would be pretty decrepit, so a weathering challenge.
The arrival of a coulple of filthy four wheelers with wooden seats would probably put the lady on the platform into a state of shock !
Cheers
Ian