I know MV sells some. Basically, you don't want the charger's requirements to exceed the USB adapter's output (but the adapter can be more). So, look at the charger cable. There should be fine print on it like input: 5v, XXXmA, output <whatever>. That input: is the draw from the wall adapter.
I'd recommend that you get at least a 2.0 amp one since you may want to use it for higher draw stuff too. 3.0 is even better.
Here's one possible link:
2 amp AC to USB Adapter
That's 2.0 amps. You have to do the math, or get whatever the vendor recommends. Also, make sure you use the same charger that came with the e-cig (put a sticky on the non-print side or on the cord that has the make/model on it).