Try a sporting goods store, and get the kind with a loop on the end (that goes around the thumb), velcro fasteners, instructions for wrapping, and the longest ones you can get.
You can also do a web search for "boxing wraps" and see what you can find, but they are so cheap that shipping would probably cost as much as the wraps.
ETA: if there is a karate or martial arts studio near you, or a boxing training center, they might sell them also, and be able to show you how to wrap them. I got my first pair from a cardio karate class I took at a karate studio. Now, I just wear weighted gloves.