Interesting model but I don't see smoke dischargers mounted on real WW2 Shermans in photos.
I do however see them on almost every photo of Israeli M50/M51 Super Shermans. Perhaps this is where they get the idea from?
(Image removed from quote.)
I agree that it is difficult to find pictures of shermans that are 1) of high quality of 2) a tank in combat rather than a static display that 3) isn't so incredibly cluttered as to make any possible smoke discharger easy to see. But,
this page has a pic of a 1944 Sherman with an "experimental" smoke discharger attached, so we know the US was at least toying with the idea, and could very well have been deployed by war's end.
This looks like the gun is of wwII vintage, but I think it is a re-enactor's vehicle.

There is also this link I found, showing a technical manual in April 1944 according to the caption (can't get the image to work). If you can read the small print, to the left of the picture in the large list pointing to the turret there is a reference to a "smoke bomb thrower." I think that might be something a little different, though.
http://www.lonesentry.com/blog/hows-your-sherman-herman.htmlAnd then there is this page of the 2nd Polish Armored Division while in Italy.
http://www.ww2incolor.com/poland/shermany-2-dp.html
Note the smoke dischargers in the tank in the foreground.
But, again, beside the point of the OP that the Sherman really should have smoke shells for the main gun.