New Market 168 at the junction of somerset st. and wellington is a great source for frozen dim sum items. All dim sum items are sold frozen as they are too fragile to work with when fresh. They have a good selection. The Noodle House which is about a block and a half east of Bronson on Somerset (set back on the street on the right hand side) is the perfect source for dim sum items. Again all the products are frozen and this place supplies many of the Chinese restaurants for dim sum.
On sommerset just past preston street is the 168 market. they have the largest selection of frozen dim sum i have seen. loblaws carries some in the freezer section. there is also a store on sommerset, few blocks east of bronson called the dumpling shoppe which sells frozen dumplings and frozen steamed buns.
the st. honore bakery on booth street (south of sommerset a few blocks) has ready made chinese buns that are very cheap and yummy.