Olympus make very nice autofocus macro lenses for Micro Four Thirds!
However, as a general rule one does NOT need to use auto focus for macro-photography as manual focus is MUCH easier, and many set a focus, and thus a magnification, and then adjust the camera to subject distance, using magnified live view to assess focus accurately.
Thus, this is one area where you can get by with older and cheaper manual focus macro lenses – although they may not be optically corrected as well as the new digital lenses.
Most legacy manual focus lenses can be bought on Ebay for under $200 and the main issue with them tends to be purple fringing at high contrast edges such as on edges of white petals.
You can use Canon EF lenses, but setting the aperture must be done on a Canon body BEFORE mounting on a different camera system which makes them not very practical for most macro work when you need to focus wide open then stop down.
Most of these legacy macro lenses (except Leica M, enlarger, Canon FD) can also be used on Canon or Olympus dSLRs, but generally, only the Nikon-mount ones can be used on Nikon dSLRs.
You will not be able to use TTL auto exposure mode flash with legacy lenses on a Panasonic camera, but this can be used on an Olympus camera.