Beretta is distributed in Canada by Stoeger (Canada). The PX4 semi-automatic was first offered in the United States in 2004. A pistol with a relatively short barrel, see photo: http://world.guns.ru/handguns/hg149-e.htm
There are Beretta Storm carbines but they are not the PX4.

It can be bought online, but Canada Customs would pick it up since it is illegal in Canada with few exceptions (police, etc.). The best source would be your local word-of-mouth dealer (as suggested by Big Mick). If one really wants one, it can be had. Gun laws don't stop the trade, probably even less effective than the drug laws.

In looking up information of Beretta models, I ran across some really weird websites, with posts from people I would never like to see within firing distance (some Canadian). Gun laws don't control the insane.