Got a wooden headboard? 2 wood screws and a cheap nylon holster will do a nice enough job.
or this:
http://cgi.ebay.com/Slip-Bed-mattress-Holster-Rack-Handgun-Pistol-/330557980055
or this:
http://cgi.ebay.com/Slip-Bed-mattress-Holster-Rack-Handgun-Pistol-/330557980055