The fabric in most suits will not support a firearm without distorting the cut of the suit, the fabric, or the "hang", unless it is a super light pocket rocket carried in a front pocket.
I would never ruin a suit in such a manner (trying to "build in" a holster/attachment or the like). It will look like you're trying to carry a small anvil.
Look at smaller pistols and quality pocket holsters. The right combo will work well in nicely cut suit pants, or dress slacks, with no one the wiser. Get a quality holster made for the gun!
There is a thread for "Mouse Guns," virtually all of which are fine firearms. Combine one of these with a quality holster, and you'll be good to go. Holsters could include pocket holsters, shoulder rigs, and others.
Look here: Small 9mm or .380?
Here too: http://api.ning.com/files/cmz-Kp*lYg...Comparison.jpg
There are dozens of nice options when wearing a suit. If you go with a shoulder rig, wear it when the suit is tailored, if your locale and environment allows.
Does anyone have a better link to the Mouse Gun Chart?