First talk to the bank. Also I assume you are going to stay max 2,3 days right? So in that case you should be able to spend your entire weekly allowance during that time. Having multiple cards too will help. I had a HSBC premier and managed to get them to allow me to spend any amount as long as my card was loaded. Also the restrictions weren't applied for lodging and medical stuff, but check them now.
No point of taking cash from black market unless you get it quite close to the bank rate. Else using CC is the cheapest.
Also if you have pre planned activities try booking them while you are in SL, that way you don't have to go and spend. Eg: you can book universal studio (you might get offers as well).
