Yes online is always a good place to look if you're looking for something specific, if you feel awkward buying them in person, or simply don't have a store near you that sells cute ones. I personally found a lot at stores like Meijer, Target, and other places like that.
If you're on a budget, some dollar stores actually have a pretty good selection too! I found a really cute Hello Kitty one and a few other cartoon-themed ones that were super cute (Peppa Pig, My Little Pony, etc) when I went to Dollar Tree last time.
You can always try the kids craft aisle or the general craft/art supply aisle at a local supermarket to see if they have anything. Good luck!!