Good afternoon, Ed.
Unfortunately, what you are looking for is the proverbial needle in a haystack. I know of a site that buys Kleinguenther rifles and this is what they say about magazines:If you are missing a magazine for a K-14, or K-15 Instafire they are VERY difficult to find. When we have them them they are very expensive because they are expensive for us to obtain. Do not lose your magazine since they are next to impossible to find!
Have you had the gun looked at by a gunsmith? There may just be an issue that needs to be worked on. If you have a photo of the gun, we can try to identify it.Jim