There are a few early films out there that come to mind.
1 - There is a REALLY early, as in 1903, film on the Georgetown Loop that someone posted about a while back - can be found here The passengers were given white handkerchiefs to wave for the cameras for the visual effect. Pretty cool old film.
2 - Another one on youtube - mostly SG colorado lines, but shows the Loop.
This one dates from 1916
3 - The Richard Jackson films were transferred to Video by WB in the 1980's and are now available from Pentrex. Quality is pretty low, but incredibly rare stuff dated from 1938 - includes films of the 1938 excursion with RGS 25, a few Silverton Northern shots, C&S footage, etc. Well worth it
4 - Machines of Iron has the Uintah film mentioned in the thread, as well as C&S footage from the 1930's - not quite as old as you're looking for, but again, rare stuff. Also some 1920's footage of the Moffat Line including Rotary plows on another DVD.
5 - Sunday River has a film called "Across the Top" with a collection of Otto Perry footage including the C&S near Kenosha Pass
6 - Many, many years ago on the forum, someone posted that there was some 1920's footage of the D&RGW owner by Coors(?) that they were aware of including footage of derrick OX and some other work equipment on the Gunnison line. I seem to recall it was not available to the public and may have been in poor shape and/or lost.
7 - There were a couple of silent films that were purportedly shot in the rockies along some of the lines, but I think that these were all shot on the SG lines only. First Hollywood films of the D&RG NG to my recollection were from ~1936 like the Texas Rangers.