you can go to any store that sells ac adapters and get the one that has the multi plugs at the end. It lets you use one ac adapter with multiple devices and should have a knob to regulate the power from 3V to 12V
Set it to 12V and find the plug that fits in the lillyput and your good to go, im using one right now.
the adapter plugs that come with the ac adapter look like this
you just have to find the one that fits the lillyput, the one i got had like 12 of these things, the more the better that way you know one should at least fit.