Duels and banned cards

Can please someone explain to me how the “banned cards from duels” system works? Why banned cards like wildfire can be offered and also can be discovered and a card like ice block or sister svalna are nowhere to be found? This complaint is more for Reno-wildfire decks which is ridiculous !

Banned cards are simply banned during the deck building process. Finding them in card buckets is different. Not sure about Ice Block specifically, but I know Svalna should be able to be discovered so I think you just got unlucky, assuming you had cards from the same expansion she was in.