I understand what you are saying. The hardest part to build an aluminum case is to digitize the case into a CAD program, and know what bit sizes to round out the corners, especially the inside ones. As you know, since you are asking, once you have the file, you can make as many as you want. It could cost upward a few hundred dollars to laser scan one, and many more hours of labor to fine tune the file through trial and errors. I would be happy if imsto would share it. I don't think him or anyone is obligated to. Why would you think he is not out to make a buck?
If it was so easy to create the CAD file and that it is not a secret, we should be seeing plenty of these aluminum cases for all kinds of keyboards already.