There are no teleconvertors for mFT yet, and the most likely reason is that are are not yet any mFT lenses that could make much use of them. TC's are only of much interest for use with moderately long telephoto prime lenses or with lengths at or near long end of a telephoto zoom, and with those lenses having minimum f-stop faster than about f/5 at the focal length used. With a slower lens and with TC attached, the lens speed drops to a painfully low f/7 or slower, making focusing hard for one thing, and most (not all) customers for TC's are interested in adequamte focusing speed, for wildlife and such.
AFAIK, there are no native mFT prime lenses long enough for many people to want to use them with TC's, and all the zooms with significant telephot reach are f/5.6 or slower at the long end. by the way, note my correction in the subject line about the Panasonic 100-300, which is f/5.6 at thr long end, not a constant f/4.
I predict that TC's for mFT will only come with or after the arrival of faster telephoto lens options, like the native mFT 50-200/2.8-3.5 that I dream of.