Can confirm Devon Avenue is a good bet - I live over there. I've seen those rock hard mangos you speak of lately, however I can usually trust that at least one of those stores on Devon will have some ripe options available. Mangos are a staple for me and I haven't had to go without yet this season.
Also this might help someone - for ripe sweet mangos you want to look for a good amount of green on the outer skin in addition to some red/orange, and they should be soft obviously. I think I read that they shouldn't smell too 'sweet' - that's a sign they may be overripe and the flavor will be bland.
Logan: Come on, everybody, wang chung tonight! What? Everybody, wang chung tonight! Wang chung, or I'll kick your ass!