Note: you'll see this effect any time you have a tonic-containing drink under a blacklight. See How to Make Edible Glowing UV Reactive JELLO, for example.
Step 1: Ingredients
I bought the flashlights from DX as "UV Money Detector LED Flashlight Keychain 10-Pack" for $5.24. Allow a couple of weeks for them to show up. You can buy them at the dollar store, too.