Why don't you just give the card details through PM, as they are for online purchases. ?
i´m NOT offering some stolen credit card numbers from Russia, i´m offering physical cards.
If someone want to make cash withdrawal, he can, but only in country of origin of the card: Czech Republic (EU).
Also see the "real" thing and have it in the hands is better, than some virtual number i think. But, maybe i´m wrong...
A lot of people wouldn't want to use the cards for withdrawls, and would be happy being able to spend it. Also, since you are doing a giveaway, a digital card for the giveaway for 20 cards, it might be a better option for you, as it saves the shipping cost for you. And since its a free giveaway for the 20 people, they won't be risking anything for you to use the cards, as they are offered for free in the first place. And later once you introduce the cards for payment, then you could ship the physical product.