Colleges get instructors (faculty and TAs) from a wide range of regions, so there will be no escaping encountering instructors with accents other than what he may be used to (including from different regions of the US, or other places where English is the most common first language such as England, most of Canada, Australia, New Zealand, etc.).
Rather than approach it in terms of instructor national or ethnic origin (which is impractical and could be seen as advocating some type of illegal discrimination), you may want to investigate whether there are disability accommodations that are possible (sometimes with existing services, such as notetaking/scribing services found in some larger lecture classes at some colleges).
What may also help would be to move to an area with greater (domestic and international) immigration, so that he gets used to more different accents in daily life. But that may not be practical for you and your family for other reasons (cost, need to change jobs, etc.).