My catalog reprint collection is somewhat haphazard, but the 4.5" version was offered by Abercrombie & Fitch in their catalog in 1910, so one would expect a certain amount of civilian sales. (First picture)
The Schoverling, Daly & Gales catalog from 1915, however, offers only the later standard lengths of 4", 5", and 6". (Second picture)
Of course, two data points are thin for any conclusions.
Thanks Absalom for the catalog pics. Makes sense that Colt would not had offered all 4 barrel lengths at one time but later settled on 4, 5 and 6 which continued all the way into the official police MKIII.