I, too, have been unsuccessful in finding a macro or free plug-in to create any gear you need.
What I've found to work best barring that is to search SDP-SI (
www.sdp-si.com) for the gear I need (if it's standard) and use their models. The models they have available for download often include one or two modeled teeth which you can then revolve around the gear and make a complete model.
Also, remember that unless you're doing this for rendering purposes, it's a lot less taxing on your hardware to model gears without teeth and makes mating them much easier.