Thank you for your welcome and reply Vince53,

The controller is definitely separate from any power supply, as it has a 2.8mm barrel socket in the back.
The set is shown on the Lionel website, but no information for the set (spares etc) are shown.
https://www.lionel.com/products/ls-thomas-the-tank-engine-set-8-81027

I have attempted to contact Lionel via email on several occasions with no response unfortunately, and so I was hoping someone on this forum may be able to shed some light.
I do realise that the set is an ancient one!