As I said, finding decent locomotives is a challenge. Jamie Bothwell suggested me to take a look at Bachmann's On30 4-6-0, saying some driver conversion kits do exists. It certainly would be an interesting way to get a unique small steamer at a decent price.
According to specs I could find, the Bachmann locomotive would have, in S scale, 60" drivers while the prototype had 51". Pilot wheels are also a little bit on the large size. Otherwise, the rest of the locomotive seems to be a fairly good starting point. Most parts could be kept, dome would have to be replaced, the smoke box shorten and cab highly bashed if not scratchbuilt. The tender wouldn't be a particular challenge to convert and its trucks would be swapped.
I will have to gather more information about the On30 locomotive to see if the overall size is compatible with TMC #8. I've located the CNR locomotive data sheet and will be able to make some comparison. If it is within a decent margin of error, I guess it could be a possible way to get some motive power for the line.
Meanwhile, I decided to slap together a quick little cyber kitbash to see what could be done. So far, so good. For the paint scheme, I'm not sure #8 had white tire in service. It was a common photograph gimmick used to get better contrasting builder photos. On the other hand, it does look extremely nice and would fit the era.