If you can lose $6k on Blackjack, it must be possible to make that much back again. You obviously just went through a run of bad luck. The best advice is to find another credit card, deposit another $6k and make big bets until you get to +$12k. Make sure you invest at least $1k on each bet though, as you need to increase your volatility so you're more likely to reach your target.
Alternatively as already mentioned, you could try roulette. If you bet $2000 on Red twice and win (investing the winnings from the first go in the second bet), that's all it takes to make $6000 profit. Of course there's only a 25% chance that this will work first time, but because it's a 25% chance, on average it should only take 2 gos. Which means $4000 invested on average for a $6000 average profit. Take the average profit from the average investment, repeat 3 times, and you've made your $6000 back, almost guaranteed.
An alternative strategy would be to go to borrow $60k from a trusted friend or relative. E.g. get a great aunt to remortgage (you could say you're setting up a business). Go back to roulette table. Don't do black or red because it's only a 50% chance of winning, but instead cover 90% of the numbers on the board with equal bets, and you'll either win back your $6k (90% chance), or lose the whole lot. If you're thinking of taking off to South America anyway, this doesn't matter too much, and there's only a 10% chance of this happening - you'd have to be REALLY unlucky to lose it all.
Good luck!