I do believe Atelier Bière & Vin carry 64oz growlers. You might want to give them a call, but new bottles are really expensive. They are in Longueuil.
If you want swing-tops, there is currently 64oz bottles of Grolsch beer on sale at most Costcos.
Most specialty shops like Le Goblet in Vaudreuil or La Consigne in Ahuntsic might have used ones, as I know Brasseurs illimités bottles its 100IBU Cascade IPA in 64oz growlers. If not, there's this new place downtown called Biermarkt, but I really don't know what that shop is about.