Stacking swivels were not used after WW1 and never on No 4's. A few NZicon surplus No 4 fore-end sets are occasionally turning up for sale here and are selling for NZ$150-200 at auction. Postage would probably bring the price to the same amount in US dollars. I can keep an eye out for a set and advise you if you like. The NZ No 4 bayonets were often not marked at all, and those that were had a crude N^Z applied with an electric pencil to the side of the socket.