The best way to get missing legendaries?

I'm a mostly free to play player. I do buy the battle pass every season and do my weekly quests. I finish the pass and even do the events. There are still so many legendary and epic cards I'm missing. Maybe my pack opening is just really unlucky. I don't dust until nerf patches come around and have crafted a good chunk of the DK cards as it's my favorite class. I'm out of dust and gold and wanting to try other classes but I just don't have the cards to play some of these fun seeming decks. Is there some more optomal way to get more of the cards I need? Am I just stuck opening packs when I hit 100 gold and hoping for the best?