We've had much good luck with MG to HG kids who are 1-2 years older. They're easier to find than HG+ kids the same age, the age difference isn't so noticeable when it's only 1-2 years, and interests are often well-aligned when it's GT families you're dealing with.
After 5+ years, DS8 is still good friends with a boy he went to preschool with, a neighbor, and a family friend, all of whom fit the pattern of being 1-2 years older and MG to HG.
If you can find a mixed age preschool where your child is one of the youngest kids in the class, it can make for a better hunting ground in my experience.
HTH!
