Forget the internet. Leg work is needed. Try ringing your farrier, who knows everyone. Tack shops, feed merchants another. Otherwise, drive round your local area and pester everyone with horses, they will know someone who knows someone. Farmers are looking to bring in extra cash and may provide a small yard.
I think you just need to be extremely proactive in your search and spend a weekend in your car searching your area and talking to people.
I have been looking for ages and ages as want my own yard and I never seem to be able to find anything, Lisa found a yard with 5 stables, menage with good grazing in Chobham but was a week too late!
I am in the perfect position to do it as well at the moment!
You could try an ad in h&H. I have found the local add mags to have a good equestrian column and seen loads of yards advertised in our area.
For what you are looking for, the owners are'nt really going to respond much to adverts, they will want word of mouth and to see people face to face. I think you will have far more success doing the leg work, getting out and speaking to people. Ring your farrier, they know everyone!!!
Try contacting a local land agent who deals with farms/farmland in your area - e.g. Strutt and Parker - tell them what you are after & they will contact you if something comes up.