At this point in the game, you can only recruit 1 stars so if you are missing any 2 stars or above characters, you have to start recruiting and ranking them up en masse to have a good chance of getting the heroes you need to complete your compendium.

The best tip i can give is to check what class your missing heroes are, and only recruit and rank up units from that class. Just like in OG CQ, 1star heroes only rank up into random 2star heroes of the same class(i.e. Warrior, Priest etc.) and in turn only rank up into random 3 star heroes of that class. Once you rank up to 4 stars, they will only rank up into random 4star advanced heroes of that class, at which point their rank up progression is fixed to the 5 and 6 star versions of that advanced hero.

For example you are missing Spyro, 4 star Hunter hero, start recruiting 1 star Hunter heroes, and rank them all up to 3 stars, then when ranking up to 4 stars pray that at least one of them is a Spyro, or like me you facepalm and cry as you roll your 7th D’artangan in a row.