Protection of Jerusalem (Pa) is the only way I know. Pleading for the City is a great way to search out the set aside angels.
Protection of Jerusalem (Pa)
Play as: "Set aside two silver brigade Heroes. Protect one Fortress from discard while both Heroes are set aside."
Pleading for the City
"Set aside a Hero for one turn. On return, you may search deck for up to 2 silver Heroes and place them in hand, and search opponent's discard pile for all Lost Souls and place in his territory."
Kirk