Call Dehners & see if they have any orphan boots that match your measurements?
If you are looking for short, schooling boots, the Ariat Terrains have a nice wide toe box. And seem to run large, so fitting shouldn't be too hard. I normally wear a 39 these days, but the best fit in these was a 37.5.
I need size 8-9 super wide feet (triple E) wide calf and tall. Mountain horse have always fit well and they run $200 to $300. I also found some Ovation for $200 that are front zip dressage high boots. With size 11 feet, you should have an easier time than I do. If you just measure you feet and leg according the the charts they have, it works really well. This is coming from someone who has a REALLY hard time fitting shoes. I had custom Dehners from 25 years ago, and when the Beagle ATE them, I had to try ordering online. It's worked really well.