Debate rages over whether improvised weapons are weapons for the purpose of the masterwork quality or enchantment. As of yet there's no clear answer.
The deadly dealer feat states the following:
Benefit(s): You can throw a card as though it were a dart, with the same damage, range, and other features. You must use the Arcane Strike feat when throwing a card in this way, or else the card lacks the magical force and precision to deal lethal damage. A card is destroyed when thrown in this way.
The text of the feat is explicitly clear that the ammunition is destroyed after being thrown, irregardless of whether it hits or not (unlike normal ammunition which has a 50% chance of survival after a miss).
Given that you're a sorcerer, you probably have better things to do with your standard action than throw cards anyway. I wouldn't recommend these feats unless you have no choice.
Alternatively, the Refine Improvised Weapon spell could transform a card into a throwing dagger, though it's doubtful it could affect a full deck. If you're looking to have the ability to roleplay your sorcerer pulling out a card and throwing it into a solid object using legal game mechanics, this is probably a better option than the deadly dealer feat.
Only when they're thrown. They're not masterwork at any other time. And they're destroyed when they're thrown.