“We should be doing this ‘seeing the good’ exercise when something we consider to be bad happens to us.”
But the Shulchan Aruch (I think OC 230:5) says one should always be accustomed to saying, “Everything the merciful one does is for the good.” Always. (It doesn’t say “always, except for the 9 days.”) Gamzu l’tovah is equally true during this time, so I think there’s nothing wrong with looking on the bright side even now (provided we’re mourning and decreasing our joy as required, etc.) Believing everything is for the best is a basic facet of emuna and bitachon, in which we are obligated at all times.