Do you mean, it isn't in an in-game list to choose the map from?
I don't have UT2kx, but in Star Wars Repubic Commando, you can open a command menu (pressing the `/~ key) and type "open [map name]," press enter, and it will load the map in-game.
If you cannot do anything like that, I have heard there is a way to modify your map list to include your map on there. I do not know how to do it, but this is my 2 cents :] I hope it helps somewhat.