There are some great single player mappacks available SL1c3r

Kingpin: Final Crime by Method.

KP:FC includes new maps, characters, sounds and cutscenes. It starts right where original Kingpin ends. Blunt (the chick boss) flew away on the helicopter, but promised to be back for Thug's ass. She knew that it's too risky to go to Crystal Palace, where Thug got all his boys, so she sent her gang, Dragons, to tear Radio City up, so Thug will have no choice but to find and stop Blunt. You start the game in the back of Crystal Palace and go through a few levels, including "backyard" of Radio City, Sewers, Wharf and Blunt's Poison Mill before you encounter Blunt and pop a cap in her ass

You can download Kingpin: Final Crime from here - http://downloads.kingpinforever.com/meth_fc.zip

Btw, Method went on to join id Sofware and is now the level designer for Quake Live.

There are lots of other Single Player mappacks available for Kingpin and Kingpinforever hosts all known ones.
Check of House of Death pt 1 and 2 by Sonik
and the series of sequential episodes by Wheelbarrow (Funeral, The Chase, Gulag, Reprisal and Sanctuary)
Plus many other fine mappacks.
http://downloads.kingpinforever.com/maps/single-player-packs/

Don't give up SL1c3r who knows what might happen in the future.

Mr D