I got super lucky on Craigslist and found women's rubber riding boots (size 6.5 because my feet are pixie-small). I cut them down the middle, and then I used vinyl (I found this on sale in the home section of Joanne's fabric ) and hemmed it so it was square (and did those goofy little outside parts.) I then used hot glue, and I'm going to buff it up with some fabric glue today or tomorrow.
For the belts, I used a different vinyl from Joannes, and I got the buckles from ebay, of all places. It was some store that sold buckles on little pieces of vinyl for goth clothing mods, so I just harvested them (all eight! Lightning has two of the same on her wrists) and sewed them on. I did the holes with a belt-hole puncher (one of the most useful tools for this costume!) and then I hot glued them in place on the back of the boots.