Can I sell an advanced copy?

From your description of the facts, the figurine was not stolen or obtained in any other illegal manner. Therefore, there is no restriction on your selling the item. I would just keep records of how, when and where you acquired it should an issue arise. If anything, it may cause problems for the employee but not for you.

The only wrinkle that I see that may complicate Oscar's analysis is if the figurine company maintains the appearance of its not-yet-released figurines as trade secrets.

Just because one of its employees was given an advanced copy of a figurine does not necessarily strip away its trade secret protection -- and because you know that your particular figurine has not yet been publicly released your state's trade secret law may preclude you from lawfully offering the figurine for sale. I do not know how Pennsylvania's trade secret law would deal with that situation.

In some industries what's "new" is what sells and so by offering for sale a not-yet-released figurine by Company X you may be inserting yourself into a contentious marketplace and providing Company Y with a significant commercial benefit. I don't know how much you can sell the figurine for in that marketplace -- but if it were me I would likely wait and would certainly not advertise the figurine as a "New and not-yet-released Company X figurine!"