You can buy a shore power extension cord (the same big black #10 molded cord that is on your TM now) from Camping World or any other RV dealer. It will have a plug on one end and a socket on the other, of course. If you want to hard-wire it in place (like all TMs before 2004, I think), you could cut off the receptacle end. The terminals are simple crimp-on affairs (the yellow ones) available from WalMart or any RV store - buy the crimper tool as well. The whole thing will cost about $30.
On the other hand, several TM owners here have made the effort to retrofit their rigs with a detachable cord. This involves mounting a recessed plug on the side of the TM, and getting - you guessed it - a power cord with both a plug and a socket.
Take a look at this thread - there may be others.
http://www.trailmanorowners.com/forum/showthread.php?t=1589
The Marinco stuff is annoyingly expensive, but it sure simplified power hookup.
Bill