I recently went thru this when locating spare parts for my Mod. 17-6 4".
Try Midway:
Smith & Wesson Side Plate Screw Flat Head S&W 31 34 36 37 38 49 10 12
Product #: 193796 Smith & Wesson #: 03091B000
Remember, these small parts are only restocked a few times a year.
I make a habit of ordering misc 'consumable' (read: easily lost) parts for every gun I own so I don't have to deal with this. Sight plungers & springs are high on my list too.
The screw is on BO, but they are taking orders. Also check Brownells.
Right now, they have Mod 17-4 flathead sideplate screws in stock. They should be the same screw...check first by S&W part Number. It's part #35 on their webpage:
http://www.brownells.com/schematics/...-4-sid589.aspx
While you're ordering:
-ORDER THE BO PARTS for your parts box NOW!
Avoid places like Numrich as the screws will likely be all goobered up. Every part they have sent me is trash. I got a Mod. 17 center rod from them that had been cut and re-welded off center...useless and I waited a month.
Also: Power Custom has recently released a new product that has gotten pretty good reviews... a three screw sideplate kit for pre-1988 3 screw models (will fit almost anything blued)
The three screws are hex head so you can't goober them and also ship with the correct Allen wrench. Power now states that they do not include the front yoke screw. But previously, they said the third screw could easily be ground/filed to fit properly. they are all round head so cosmetically, they may not do it for you...however, for $5. these would work until your correct BO'd screws arrived- then toss them into your parts box.
http://www.midwayusa.com/product/470...ead-steel-blue
Hope this helps-mogwan