Became you are in an IB school and strong in math, you could see if George ends up with any openings. It will help anywhere if you can demonatrate fit.
You could try focusing on schools without lots of boarders. At many, international students are an important part of diversifying the student body. Hun and Shadyside are two that come to mind and that have strong academics. You should make sure you can be accommodated in math as you are strong.
You’re going to have to look at each school’s website to figure out if it’s really a good match. The list in boarding school review is a bit of a mixed bag.