@oralloy,
You need this (a "Waffenerwerbsschein") for ANY weapon which you want to buy in Switzerland.
For just one weapon, as specified in article 9b of the same law.
To get an allowance to buy all the arms you frequently mention (the "forbidden weapons" ['verbotene Waffen'], see article 5 of that law, you can try this via the canton, which all have different laws/by-laws to regulate such.
This additional and extra licence is for just one single weapon, too (even for 1 knife!). And additionally to the "Waffenerwerbsschein", you have to give an exact description of the weapon and name the seller. Further, your municipality has to answer (on at least[!] pages), their opinion about you and your answers in your request for getting a "Ausnahmebewilligung".
As said that differs from canton to canton. The most restrictive is the
Republic and Canton of Geneva.