The current edition of the Yearbook has a section about the KGV. On page 36, the General Rules provide a list detailing the criteria by which a member may represent their registered District. Please note this list is not complete as it omits qualification by virtue of the District in which one’s parents or grandparents were born.
The page on this website, Team Shooting correctly lists all the eligibility criteria in the 4th paragraph entitled “How do I get into county shooting”. So if you are looking for an opportunity shoot in a county team, please note there are potentially 9 different Counties / Districts open to you.