Skeeter Skelton reported that because the 29 was in such high demand, and each in the production run was already accounted for, when the producers contacted Smith & Wesson they refused (ethically) to pull one off of the production line to give to Paramount (sic).
An armorer then picked out the pieces and assembled one by hand so the producers could have the hotter-than-a-Texas-summer model 29. It served not only to cement the S&W brand name but to further whet the appetite of Maggie hunters even more.
Interestingly, Skelton reports that within months of the first Dirty Harry movie coming out, one could find many examples of 29s fired less than one box of ammo. Apparantly they didn't take seriously the warning that if fired correctly (perhaps the line should have been "incorrectly") it would remove fingerprints.
If you want a citation for this reference, I'll look for it later. It's either in HOGLEGS, HIPSHOTS & JALEPENOS or GOOD FRIENDS, GOOD GUNS, GOOD WHISKEY.
Q