Are there LEGO compatible CAD Files For Injection Mold Manufacturing?
Look here: http://www.thingiverse.com/tag:LEGO

But be aware- as a single person manufacturing a LEGO compatible item, you might be open to litigation. You would probably win, but winning very frequently bankrupts people either way. Do you really require a unique piece that LEGO does not make? There are many custom sets around that are a kit of LEGO manufactured pieces.