[davemc]

On eBay. I've seen several, but only one NOS. One hint: the seller may not list the battery in the RADIO categories! You may have to setup searches in several categories. You can leave the NOS or used (dry) battery in place, add the filter cap in its place, and run the set on AC. You may have to adjust the value of the capacitor so that the DC output is 2 volts under load. If the capacitor is too large the voltage will be too high. If too low, you will get vibrator hum. I also had to replace the rectifier in mine.