There are aftermarket TTL flash chord you can buy which should work as long as they're compatible with the Panasonic/Olympus TTL protocol. I just picked one up off eBay for cheap. AFAIK none of the Panasonic MFT cameras have a wireless flash trigger built in, but you can attach a remote trigger to your hot shoe and do your triggering that use using remote slaves. You can also remotely trigger flash units using optical slaves triggered by your camera flash.
You can also use Canon TTL flash cables. While Canon TTL flash
protocol isn't the same as Olympus TTL protocol, the cabling is wired the same way. Canon flash cables are more easily found than Olympus flash cables.
I have an Olympus coiled flash cable (2m length) and a noncoiled 3.5m cable I found on Ebay. Both work very well.
Another strategy if you're handy with soldering is to acquire an Olympus flash cable, cut the ends off and fit them with RJ45 female sockets. Then you can use standard ethernet cables in a variety of lengths to connect the two ends and come up with nearly any length you want.