It turns out that there used to be. Bernat made some a while back, but you can't get it anymore. I really wish they would bring it back, because it's rather cool. I found suggestions for fishing wire or a parachute rope, or a plastic yarn, but that wasn't what I was looking for. I wanted a yarn, cotton, acrylic, whatever. But a yarn.
Then I found this blog post about making your own. Hodgepodge Crochet
It was exactly what I needed. And it worked. The theory is to buy at your local craft store a glow in the dark fabric paint (it doesn't matter what brand), soak your skein of yarn in water, dump the paint over it, and mix it in. Let it dry, and rinse out.
|I used this brand, it has a little yellow tinge to it|
And this is craft paint, it is non-toxic, which is what everyone asks if my yarn is now dangerous. Nope, it's fabric paint, so it is completely safe, just follow the bottle's instructions.