The majority of c02 guns are fixed slide, however there are a few companies out there that make green gas guns that can use c02, however it will wear down the internal components at a much faster rate unless they are replaced with sturdier internals right off the start, unless the parts are reenforced fromt he start. Im sure there maybe one c02 out of the box ready m9 out there, but Im not sure who makes it or even if it does exist. Although Im sure theres probly one.
You may find it difficult to find a walk into style shop for airsoft in Canada, the majority of airsoft sales are done online.
If you are interested, you may wish to look into this websites age verifacation system.
Where if you meet the requirements you can gain access to a small list of retailers and this websites classieds section.
Please read here for more info.