Try "horse sneakers" website. Am sure you can google it. I have been to the website, just not lately--they are in AZ, will custom make hoofboots to your measurements; the boots can even be resurfaced. They are pricey, as I recall, but sound like a good possible choice, esp. when nothing else will do.
(I have been able to 'work on' a set of older Pony sized Easy Boots[they don't make a 'Miniature' size, even though some miniature supply websites advertize them as such; the 'Pony' size IS their smallest, and start at @ 3 1/8" X 3 3/8"--- ]. By shortening the heel strap permanently, and placing some 'bushing' inside in the form of a piece of vinyl padding, I have used these on several of my 33-34" horses. It still isn't perfect-they will occasionally come off, so need to be 'watched' -but have helped when the road is 'gravelly'...)
If you do try them, please come back and share your experiences with them!
Margo