Are there any available contact details for the two farmhouses in Huangyaguan?

Lucy, I got two for you. One is Chunzi Farmhouse, which is around five minutes' walking distance to the ticket entrance. Tel: 15822557318 13752363780. The other is Fu Lai Shun Farmhouse, which is claimed to be just around 300 meters to the ticket office. Tel: 15620783699/13752343415

You should make a call to confirm how close the farmhouses are close to the wall. The above information is acquired from their websites (Chinese version only).