If you can't get a draft horse farrier, maybe you could buy size 7 shoes and big nails, 9s or 10s, ask when you are buying them; also get Capewell nails, if you can), and get a regular farrier to put them on. It would be ideal if the farrier had a big set of clinchers, but the regular size will do. I lucked out and found a real good set at an antique show for $20. The seller had no idea what they were or what they were worth. The buy of the year! My farrier has the exact same type, which he inherited from his father.
Try Nick Young he is in Sanford/Carthage Area-if you tell him the size he can probably get the shoes.. He is great!
Judging from the work I've seen him post on horseshoes.com, Nick Young is a capable hand in the fire. He should be able to hand build any shoe your horse needs if he doesn't stock it in pre-made shoes.