What you need is a 1993 and up ZX-11 engine. (the D model)
In 1993, Kawasaki made both a ZX-11C and a ZX-11D. From 1994-2001, it was all D model.
Since Kawasaki made the ZX-11 for SO many years, they are relatively easy to find parts for. Some good sources are E-Bay and any motorcycle dragracing forum. The ZX-11 is a somewhat popular engine for recreational use- dragracing, sandrails, midget sprint cars, etc. So, you might want to try any forum with those kinds of focus. Also, virtually any salvage yard that carries Japanese bikes/parts will have a ZX-11 engine lying around. (do a google search on "motorcycle salvage"- you'll get dozens of places. Figure on having to spend about $1000-$1500 for a complete engine.