You need two seperate supplies.
For the 5 volt usb trigger, the easiest way to do that is just use a powered USB hub. Just plug the cameras into the hub and add a switch on the 5volt line going into the hub. (don't hook the hub up to a computer).
For the cameras, I tried this item from amazon.. Its an aftermarket unit, much cheaper than the official onehttp://www.amazon.com/gp/product/B000XQ ... ss_product
However, I didn't have the best of luck with them. One of them worked, but the other didn't.. They sent a replacement but that didn't work any better. I ended up taking the end off the one that didn't work and soldered it to the good one. It appeared that the voltage was too high. The OEM one is rated at 3.2 v. The aftermarket one seemed to be putting out 3.7 v. (though it was rated 3 volts).