Hi,
Just bought a full gear set at Modelsinmotion.co.uk
FastFind: V5XU4 K35518 KO Plastic Gear Set For PS2113
Also a recommend on this forum, which I only saw after I had paid for the plastic set, is to fit the 2123 metal gear set which apparently also fits.
see
http://www.oople.com/forums/showthread.php?t=14738 , Post #9