This is a picture of the gate, we bought it at Tractor Supply. We just built a cage using cattle panels and t-posts. I would recommend using smaller mesh panels because the real small ones get out of this one.
We have another trap that has a drop gate but only catch one at the time. We have caught several deer with the drop gate so we stopped using it.
http://i143.photobucket.com/albums/r125/thomaswilks/2013-01-08154828.jpg