Any 18VA (or higher) transformer that outputs 30VAC will work. If in the states, you need a 4:1 step-down. Japan would need a 3.3:1 step-down and ROW (rest of world) needs an 8:1 step-down.
Then, all you have to do is find the right plug. Make sure to measure diameters for the the post on the inside and the hole.