1) What does one do if he said the Bracha of "Baruch Dayan Ha'emet" upon hearing of the death of a close relative (eg. father), when at the cemetery does he have to tear Kriyah? is it appropriate to wait for the bracha? 2) As Kriyah seems to be a Mitzvah Dirabanan, why don’t we say a Bracha of "Asher Kidishanu ... Al Ha Kriyah" or something like that?

1) It is not a simple matter. You should go by the Chevra Kadisha's directions. 2) We do not make a Bracha on a bad event. Rabbi Yitzchak Grinblat