Unfortunately, I'm having the same problem in London, Ontario. I've checked in all the places I've purchased the store brand of "Rogaine" from before (Rexall, Shoppers, Walmart) to no avail. I was able to purchase Rogaine (at a terrible price) from Loblaws. I actually bought the last 2 boxes they had but when I got home, I found that one box had been opened and the Rogaine had been removed.
I would appreciate any leads on where it can be purchased.