I totally sympathize! I'm 5 ft 2, and I looked for weeks for boots that would fit right. I would look on eBay if you have measurements. Sometimes you can find lightly used custom boots there. If you can (or haven't yet), try to get to a tack store and try some on. I actually ended up buying a pair I tried on in the store after I discovered that what sounded like it would be too big fit about perfectly, especially after being broken in. They will be too tall at first, and painful unil they're broken in, but the height will drop by as much as 2 inches for some boots.
I have also seen half chaps, I think Ariat was the brand, that are designed to look like the uppers of tall boots that may be an option (I've never seen them in person or being used, though, so I don't know if they look enough like tall boots for showing).
A stubborn horse walks behind you, an impatient one in front of you, but a noble companion walks beside you ~ Unknown