I think that starting from zero knowledge to a sellable product this summer does not look very realistic 
At the same time, if you are motivated enough, you could start to learn how to make your own custom.
As @skepp said 3d printing is a good starting point, and some custom keyboards that are sold are 3d printed like Keyboardbelle did.
Another way is to make acrylic stacked boards, one very known designer @qlavier is using this technique.
The CNC option is a bit more involved, need a minimum of CNC manufacturing knowledge and requires the use of professional CAD tools like Fusion360.
Also making a CNCd case is hella expensive, the other 2 options are more budget friendly.