I know very little about Colts, but spent a few minutes searching the web, don't know if this will be useful to you or not. Apparently due to slowness of supplies arriving in Mexico at the time, Walker's unit allocation of the Walker revolvers was still crated and in Vera Cruz, when Sam Colt sent Walker a pair of them as a gift. Walker was killed four days later.
There's a recent book out on Colt:
Samuel Colt: Arms, Art, and Invention By Herbert G. Houze, Yale Univ. Press, 2006.
I could not get the part of this I wanted to pop up on the web, but it seems that on pp. 75 there's something about Walker's personal gun or guns, and a question regarding the attribution. Hopefully some other member will have this book and can fill you in on what it says.
The article Mr. Houze footnotes more than once is:
Philip Schreier, "Walker's Walkers-The Colt Walker Revolvers of Captain Samuel H. Walker, Texas Ranger" in MAN AT ARMS v. 20? No. 3 May 1998 pp. 30-39.
I'd begin by checking the book first since the information is more recent.
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