Yerba Mate Gourd/Bombilla
Any of the Latin stores in Kensington Market should have them.
Outside of downtown, there is Market Tino at Keele & Lawrence, Emporio de los Sandwiches on Wilson b/w Keele & Dufferin, and there is a store on Jane south of Wilson called Gaucho's (I think)
I love Mate, but as I am no purist, Market Tino sells Cruz de Malta tea bags (mate cocido) that have been very convenient for me. I haven't yet seen these anywhere else, but then again I still have a large supply, so I haven't been shopping for it.