hello - might be worth looking on www.berkscountyrc.co.uk - they list details of events on there...sometimes there are sponsored rides but not very often.
Also just looked at Mortimer riding club which does have a sponsored ride but not until Sept - www.mortimer-rc.info/
This link - links you to all the riding clubs in Berkshire. They list events on their websites and you should find a couple of sponsored rides within the area. Highclere near newbury have quite a few too. http://www.equine-world.co.uk/links_show...me=Riding+Clubs