Tools: digital calipers, Rhino, 3D printer
Materials: Spool of ABS or PLA plastic
Step 1: Digitize
The first real step is to regain your composure and chill the eff out. Also, don't worry about buying a new keyboard (and good luck trying to get just a single component from the manufacturer). All you really need are digital calipers. Measure out your broken buddy, or better, remove the intact one depending on damage inflicted.
I personally prefer Rhino, but any 3D modeling software should be fine as you need an STL file at the end. You can also use our 3D scanner or AutoDesk Catch if you aren't as comfortable with modeling software, but it won't be quite as precise.