Reproductions made in Taiwan (probably) have appeared in recent years. The earliest ones had the Auto Ordnance name and trademark on them, action by the present holders of the trademark saw that removed and more recent ones have been unmarked. The Crosby name has also been on some of them. These repros do not have the rotor packed with grease, unlike the originals, so you have to do that yourself (a tool needs to be made to do this). Some have had to be 'doctored' somewhat to make them work reliably.
You should bear in mind that the bolt needs to be retracted to fasten the drum, so if the gun is one of the more recent deacts which does not do this it will be money wasted.

Reproduction Thompson Accessories Reference Guide - Thompson Submachine Gun Message Board - MachineGunBoards.com Forums
Greasing a new reproduction L drum - Thompson Submachine Gun Message Board - MachineGunBoards.com Forums