My curtains are held up by these wooden hook like objects that are
each held up by one screw that is screwed into the ceiling. The
problem is that these curtains are of the heavier variety, and they
are pulled down on the screws and my curtains fell down. In other
words, my ceiling sucks because it can't hold screws (even with the
screw holders) if there's substantial weight on it.

Where can I find an alternative do-it-yourself solution in downtown
Toronto, Ontario?

Could you put the screws into the ceiling studs?  Then they shouldn't
fall out.  If your ceiling studs aren't in the right location, there
exist toggle devices that might work.  These are like collapsible
wings that attach to the bolts.  You make a large enough hole in the
ceiling that the toggle can fit through when collapsed.  Then once you
have it through the hole, the toggle opens up and spreads the weight
over a larger area.  A hardware store should carry these.  Probably
someone else will know the correct name for these devices.