Here's an idea. A couple of years ago, there was a bunch of folks involved with the solstice/equinox accessess at Stonehenge who were looking for a site for a gathering either side of the summer solstice. The plan kinda faded out when a site couldn't be found.
If you think that there's a good chance of getting something together near Yatesbury (or anywhere else nearby), I could put you in touch with them?