I am looking for information(books - articles - magazines), about the Smith& Wesson 25-2 .45ACP, 4" barrel. I have seen plenty of "Rare" 6 1/2" and 6" barreled revolvers on GunsAmerica and Gunbroker., but no 4". Anyone with an idea on numbers produced or the possible availability? I am not currently interested in a 25-2 in .45 Long Colt, I have seen plenty of those also. I want a revolver stablemate for my Officer's and Kimber. I'm not interested in a new 625 either.

The 25-5 is the .45 Colt version.  All 25-2's are .45ACP.  The 25-2 originally started life as the 5 1/2" M1917.  The M1917 turned into the Model 1950 target (which had a tapered 6" bbl and adj sights), and that turned into the Model 1955 (which was the same as a Model 1950 except it had a heavy barrel).  The M25-2 is the Model 1955 under the newer model number scheme S&W went to.  Because of this, most M25-2's are 6 inch barrel guns.  

Towards the mid 80's they wound down production of the M25-2, though I think they listed it available for 4" and 8 3/8" as well, but I may be wrong.  Seems at the time they didn't sell well at all.  The M25-5 continued production after they dropped the M25-2.

Since then they've come out with the various newer 25's in both .45 calibers.  

I can't help you with production numbers.  The 4" N-frame never proved a big seller.  It did OK in .357, and decent in .41 mag for service use, but most demand at the time was for a longer barrel. Since the gun was already a big one and was mostly used for target work, rather than service carry, most people wanted a 6".  There were some snub-nosed variants for Lew Horton, etc.

Ross