Good luck trying to find one of those! Unless you're absolutely set on an original rear sight, my recommendation would be to obtain and fit a good "one piece" rear sight, such as was provided in the MK I and/or MK V models. There's a pretty close copy available from Brownell's these days, but it's not cheap (about $40.00!!). It's certainly just as rugged, and has serrations on it to reduce glare, which is kind of a nice touch. It also has a wide enough notch to accommodate the wide front sight, which sets it apart from other sights on the market. It's tall, so there's room to file it down if you're hitting high with it. I've fitted one to a MK VI and the owner seems to be very happy with it.