Saw some at No Frills at Albion/Finch. The one to drink advertised to just stick a straw into it and drink ($3.50) and they also had the hard shell ones that you cook with. Most Asian/West Indian stores have them but may not find them every week.
The flea market on the west side of Dixie Rd., north of Eglinton Av. They've got a produce market in there with fresh coconut, along with other tropical stuff. They'll hack the top off a coconut there for you so you can drink the contents.