Hi ashfordmum. I too have local knowledge and may be able to help. My first thought is there are GS's locally to our area you won't have a problem at all getting in to...... However you will have preferences and it would be wise to explore all the options you can. It isn't all about achieving a 'GS' education and I would strongly advise you to go and see some school's you had previously not considered but which are in reasonable travel distance for DS.
Feel free to PM me if you want to discuss 'sensitive' details which may not be suitable for the forum