you can cehck ebay for a cable like that , its possible they will have one , or you can contact the manufacture and explain to them the "dog" ate it or you lost it in a move and they will likely comp you one.

as far as using one input and wanting it to be able to switch video sources you can do some fancy work with a few sets of cheap RCA's and some relays or you can get a video switcher similar to this one:
http://cgi.ebay.com/ws/eBayISAPI.dll...784045713&rd=1