FormerHangie
En-Route
I would presume that any DC-6 or 7 still flying would be used in some sort of an airshow act, rather than a flight op, but I could be wrong.
I don't think there are any airworthy DC-7s right now. A fellow in Florida got one going a few years back, but it broke an engine and was parked at Charlotte, I believe it is still there. It takes cubic dollars to keep one of them going.
As others have mentioned, Everts and Buffalo still operate DC-6s on a regular basis. There are some others flying as well, Red Bull has one. I don't know of any that are offering dual.
I realize this is kind of going another direction, but how about getting checked out in an L-39. It looks like it would be more fun to fly anyway: