Secret Weapon Miniatures are now accepting pre-orders on their Oni Mask Head Swaps.
From their announcement:
The new Oni Mask Head Swaps are available to pre-order at 10% off until they start shipping.
There are two sets of five heads. One set without helmets and one set with. The helmeted heads are fully compatible with the Secret Weapon helmet crests — as shown with the inclusion of a Small Roman Helmet Crest in the photo above.