If the school is at all cooperative, you may be able to visit the school and meet the new teacher(s) before school starts. Even if it's just a couple of days early (during teacher prep days), it can make a world of difference. My grandson has been able to do this not only when he switched schools, but even when he was just going to be in a new classroom with a new teacher. His anxiety about the changes is so high, that he really needs to be able to meet the teacher and see the new space separately from the crush of "first day."
Since it sounds like you're going to be moving at the beginning of the summer, so you'll be in your new town during the summer, you may be able to meet some of the families in your son's new school through some local community events and outings (to parks, libraries, etc). Maybe the school would be willing to give you the names of some of the children who will be in your son's grade and who live near you (with their permission, of course). Some libraries and bookstores have story time, when they read to children; some playgrounds have events for children; if you are religiously inclined, your house of worship may provide you with a point of contact for meeting other families with children close in age to yours.
If you haven't done so yet, you may want to find out if there is an online "community" in your new town, where you could start to find out about resources.