Try John Whinnett, has a web site www.johnwhinnett.com he is very fair and if you give him the details of what you want (shopping list!!) he will find you something suitable. If you don't get on with what he finds he will find you something that you do. I would recommend him to anyone.
Just a tip, make sure your horse is relaxed before you give it as once the heart rate goes up it doesn't work so well also has no effect on some horses in my experience!