B&H always a dangerous place to go. Not sure what camera you use, but AW has always been good for me. Or your can do a custom white balance. Just the first google page I ran into, gives you a good tutorial on a DIY with a simple pringles top.
You can also use a coffee filter. For me I actually sandwiched a coffee filter between 2 pringles top. I found that it works best for me.
There is this too
But they all work the same.