A good way of getting cab pics is to get in a cab!!!
Go for a ride on the Severn Beach line or one of the quieter Valleys lines and ask a friendly looking member of the traincrew if you can get a few shots (best to do this when waiting at a turnback point - much more likely to get in the cab for a sensible amount of time and the pics will be sharper as you are not bouncing all over the place!! - it is also polite to explain why you want the shots).
Just take care where shadows / sunshine are as if these will mess up any attempt at photorealistic cabs and be sure to take as many shots as possible of all parts of the cab.
Give me a week as I have a 144 (same?) cab pic from when I went on the Leeds meet, however it is on My Mum's Laptop ATM. It is away as she spilt Coffee over it, then took it apart & lost the Function Key :roll: