I have found it a couple of times at different spots at the St. Lawrence Market. Unfortunately the names of the spots have escaped me - I beleive I found it the last time at Scheffler's Deli in their dairy section.
I'm not sure about quality, but the IGA at Danforth and Pape has it. I remember noticing it a little while ago, but I neglected to pick any up. I'm sure lots of other stores around that area carry it, too.
there is a place on the danforth west of pape on the south side called the Greek House. They have two different varieties of halloumi. I don't know what the difference is though. I do know halloumi is great when you rub olive oil into it and throw it on the grill. Enjoy!