I'll send you one. If it works out to your satisfaction, you can reimburse me.
Oh- and FedEx just because it's convenient for me. We have an account at the gun store where I work, so it's easy to ship stuff. PM me with a shipping address and any other details I might need to ship to your little tropical paradise from the USA.
I have succeeded with making STEN and Lanchester mags work in the Colt SMG, but it's not the best set-up because the mags are too wide to allow a "web" of material between the front and rear blocks. This means you need little set screws all over the place to hold everything in there and they are easy to misalign while using. You also have to modify each mag to use the Colt mag catch.
Whether or not this would work with Sterling mags is a good question. The STENs and Lanchesters are single-feed, so the bullet heads right into the chamber in a straight line. Sterlings are dual- feed, so the round might need some sort of feed ramp or bullet guide to make it to where it needs to go.