As far as custom reeds, there is nothing to it.
They sell sheets of carbon fiber reed material.
Just get a really sharp pair of scissors, trace out the size and shape you need, and cut carefully.
The trick is to figure out what thickness/stiffness of reed material you need.
Sheets of reed material are actually pretty damn cheap. Sometimes you can find them on the local at like MX dirtbike powersports type places.