I usually find them in the Party Supplies section (with the birthday cups, plates etc...), usually near the greeting cards. They have them for party favors.
This time of year you will probably also find them with the Halloween stuff. I find that there is a much better selection this time of year. Just got tons at Dollar Tree. They had many more varieties than they usually do.
We actually do use them for night lights when we get back to the hotel. I usually hang one somewhere next to the kids bed, and another on the bathroom door. I will also set one on top of the potty so everyone can see where they are going and what they are doing!!!! They are usually still glowing in the morning. I just throw them away and we have fresh ones for each night.