Which type?
The (crappy) AZERTY ones, or the (cool) French-Canadian QWERTY with accents?
If you want the latter, there are two styles. The first one is the CSA (used on macs) that has è à é and ù keys. And there is also the other style, with only a é key and a soft key for accent grave (`).
For the former, I guess ebay.fr is the way to go (shipping is incredibly expensive though).
And for Qwerty ones, I have no clue either. Try some canadian online retailers. I'm pretty sure you won't find one in the US.
The easiest way would probably be an Apple Store. They have macs in a lot of languages backstore, so they must have keyboards too.