I saw seen a couple of frog-themed bathroom decors, so I am sure you will find some. There is a lot of animal-themed bathroom decor, fish-themed ones are the most popular ones of course. My parents have a dolphin-themed bathroom in their new house.
While you may have to spend time looking at a variety of stores and internet sites you should be able to find enough frog themed decor to fill out your bathroom's overall look. You may have to use items that portray other animals or themes as well to get frogs.