I got it from Amazon, They make dyes for either oil based fluids, or water based fluids.
I had the oil based because I was originally going to use it to detect a oil leak on my old daily driver Jetta diesel.
Instructions say 1/2oz treats 4-6 qts of oil. I put most of 1 oz bottle in. My kit came with 6 x 1oz bottles. I drove the car for about 15 minutes to warm it up and circulate the dye around. Then I shone the flashlight around looking for signs of the dye around my dirty engine.
UV flashlight came from amazon as well. They also sell yellow tinted glasses (which I didn't buy) that are supposed to help the uv dye stand out more. I could see it fine without them. There are youtube videos on using uv dyes to detect leaks for more info....
I found it pretty handy, although with my level of leakage, I should have been able to see it without the dye, but it was a fun experiment. My engine was covered in dirt and oil, as I had also had an air oil separator failure a while back, and never cleaned the engine after replacing that I wasn't sure if I had more than one leak before using the dye.
. I will flush out the uv dye oil this week when I do my yearly oil change.