Warbler said:

Perhaps maybe they should have tried to find some American actors for 'The Gunfighters'?

This is the problem with viewing older shows from modern eyes.

Doctor Who never had a problem finding actors of African ancestry because of the influx of West Indian people into the country around the time. Similarly finding actors originating from the Indian subcontinent was also not that difficult.

It became a bit of a stretch casting lots of actors from the Orient.

So while a genuine oriental actors where cast in Mind of Evil when it came to The Talons of Weng-Chiang (which is practically banned in some countries) or Marco Polo the available actors had to be supplemented with white actors in yellow face.

You can only use Burt Kwouk so many times (though it didn't seem to be a problem with Philip Madoc).

The cost of flying an actor from one place to another for a minor role was too prohibitive at that time. Until the 80s flying was still a luxury beyond the reach of most people.

There were a handful of North American actors (some of them blacklisted) who were living in Britain and they tended to turn up over and over again in BBC and ITC productions.