I'm shortly going to move to a private-ish (land owner's house close by) yard with a 4 stable american barn style doo dah, field shelter, 8 acres and a small storage barn... We're renting it as a whole...
I'd been hunting for ages though and it was purely through word of mouth - the person leaving told a friend who works with my friend and as they're both horse peeps it came up in conversation... I've no doubt it would have been snapped up very quickly if it was advertised...
Tack shops, Facebook groups for that area, farrier etc... Just get the word out as much as possible I guess... This is presuming you're looking for a small concern rather than a professional yard type set up which I would have thought would be advertised via specialised estate agents...