Hitch-Mounted Bed extender platform that allows a trailer?

Although it might be cheaper to have one built by a local fabricator (I bet your local hitch shop could use the work) there are companies out there making them.

http://www.pdsfabrication.com/GateSaver.html
http://www.dgmtailgatesupport.com/

I've seen people user 2x8's as long as the bed+gate to help support.
I've got a friend who loads it, then puts the ramps in under the RZR and lifts the front with jack stands on the ramps in the bed so the front wheels are in the air (he backs it in).

Good luck!

Not sure what you are describing but this place has just about anything there is along that line;

http://www.discountramps.com/

They seem to be a good company, I have purchased from them a few times.