Arctozolt

Hi, I have just unlocked special encounters and it's awesome, I am trying to get arctozolt my joint 1st favourite Pokémon bit I went to the cube corp crystal peaks entrance and got a special encounter of dracozolt, does this mean I can no longer encounter arctozolt

Another question what's the best way to get the encounters to show? As well as what's the best way to reroll the max raid dens