I don't want to depress you but I thought I would share my experience, I traveled frequently when DS was little.
You want to verify both the TSA guidelines and the international guidelines. The TSA allows milk for consumpution on the plane for consumption but there are lots of reports of hassles of women trying to board with a large amount of milk. You should probably plan on checking it; colder anyway, or at least knowing that you might be forced to.
I, personally, would not assume I could keep milk frozen that long. Milk that is donated is shipped frozen and processed the day it arrives. If I've frozen milk semi-defrost just flying across the US. Of course you can re-freeze it, which is not recommended. I guess it depends on the age of the baby and your comfort level. I stopped flying with frozen milk at all and only traveled with fresh milk, which is so much more flexible. Depending on how long you are going to be gone and your pumping schedule, you might want to consider it.
