Missing multiple apt-get repositories, every guide leads to me to another missing repository

Reposting because I forgot system info....

I'm trying to set up a kali netbook so that I can log in with a Yubikey (specifically YB4). The official guide from Yubico states to run "sudo add-apt-repository ppa:yubico/stable", but every time I try to run it the terminal returns "add-apt-repository: command not found".

Trying to resolve that, I tried to install software-properties-common - Nope, "unable to locate package". Most guides tell me to run apt-get update to resolve that, but I've done that multiple times.

How do I add these so that I can finish setting up the Yubikey?

System info:

Kali GNU/Linux 2.0

x64 bit

Acer AspireOne

No logs

2.0 is a few years old. So, download the latest, 2018.4

Even though it is recommending to use their repo, don't, you'll mess up your kali sooner or later. Compile from source.

Regarding the command you're mentioning, a little googling will help finding the package to install to get it.