Green Dragon is more a Farmer's Market than flea market. You'll find fresh meats and produce, plus all kinds of wares from socks and towels to watches and antiques.
It can take a few hours to explore the whole complex, mostly level grounds. It is only open Fridays. We used to go often, mostly in the warmer months, but I typically get home too late in the afternoon to make it worthwhile to go there from our current location.
You may find more to do south of Ephrata and east of Lancaster city, in Paradise, Intercourse or Bird in Hand.
www.padutchcountry.com for things to do in Lancaster County.