
You can use Call for Aid and have 0 Avengers Ally in your deck to get all copies of Digging Deep in the deck into your hand at the cost of 1 card + 1 Encounter card. The downside is this immediately triggers a deck reshuffle so all of your Digging Deep will be in the discard pile after the reshuffle and renders future Call for Aid not as useful until another reshuffle. The other downside is you have to play without any Avenger Allies which means missing out on some solid Allies like White Tiger, Kaluu, etc.
Note that if you have 2 Call for Aid, you can use 1 to trigger a reshuffle and 2nd one to get all Digging Deep but it would cost 2 cards + 2 Encounter cards which makes it not worth it.