Below is a list of stores that you can find thigh-high boots at. They are not in season yet, so be sure to check these stores again in the upcoming weeks. Keep in mind you may have a wide foot and wide calf so shop accordingly.
*Payless (Not available in US/Canada/Puerto Rico)
Look for suede or synthetic suede materials they have more stretch. Also, opt for boots that tie or have a side zipper.
*Stores I have personally purchased boots from in the past
This isn't a complete list. Comment stores I left out.