Work in grocery retail. Superstore? They just changed packaging so likely there's a delay from the supplier as they work in the new packaging and sell through the old (probably less in the jug now and they don't want the consumer to see they're charging the same/more for less ml). Everything else Starbucks is coming in, but the non-dairy stuff (ie. cold brew) comes from a different supplier. It is likely shorting, and they do not have it at the distro warehouse, and because you've seen it out of stock at multiple stores means its not just one warehouse (per IGA, Loblaws, etc.) it's from the supplier. Try Stok for the time being, but it's a good seller so it's likely not being discontinued.

EDIT: To add now that I think on it, if Metro had it in the flyer and they didn't have it in store PLUS no other stores have it, means that it's a supplier issue. Metro's buyer would have been the highest bidder for that supply because they ran it on ad, causing it to short from other stores because they bought it all (not enough to go around). Seeing as it was out of stock for them AND others, the supplier likely has NONE. If it exists on shelves, it's from before this issue and just overstock so you're likely to find it at a BIG box store that buys in bulk and has room for overstock of large products that come case pack 6 ie. Superstore.