JohnR got me going to design a sleeve to use with an 8 round magazine in a 6 round Kahr, like the PM9 or CM9. I had already designed one for a use with a magazine that was just 1 round larger, like a 7 rounder in a PM9, MK9, CM9 or an 8 round in a P9, CW9, K9, etc.
So I stretched it a bit for him. In finding a place for him to get parts, I found Shapeways to print it for a reasonable cost. So, I decided to put a couple of the base plates and extension sleeves on there and make them available to anyone who wants them.
Here is a link to the parts: https://www.shapeways.com/shops/lakelinellc
The printed parts are not as smooth as a machined or molded part. If you want to get them smooth, I will add a comment on how you can smooth them up. For magazine sleeves however, the texture is not such a bad thing as far as grip is concerned.