Slightly off topic but I've included some movies featuring Colt Dragoons also since they're basically an 'improved' Walker.
Three Amigos! has one IIRC. When Ned Nederlander (Martin Short) is going to have a quickdraw showdown with the German one of El Guapo's henchman make Ned switch his sissy little Colt SAA for a "man's gun" Walker he can barely hold up. I could be wrong though, it might have been a Colt Dragoon instead.....still a heavy hand-howitzer but not quite as huge as a Walker.
True Grit had Mattie Ross carrying her dad's Dragoon.
Rooster Cogburn: Why, by God, girl, that's a Colt's Dragoon! You're no bigger than a corn nubbin, what're you doing with all this pistol?
Mattie Ross: It belonged to my father, he carried it bravely in the war, and I intend to kill Tom Chaney with it if the law fails to do so.
Rooster Cogburn: Well, this'll sure get the job done if you can find a fence post to rest it on while you take aim.
North And South (miniseries) had some Walkers used by Patrick Swayze & others in the Mexican_American war part.
The Long Riders Keith Carradine as Jim Younger uses a Dragoon to blast some Pinkerton JBTs who killed his (uninvolved in the gang) little brother.