Where do I find valid badge codes?

Depends on what badge you mean.

Some of them are listed here: TeamSpeak Badge List (outdated)

Some are sent to one’s email (Merch Badges, TeamSpeak Jedi, Official Teamspeak Gamer).

Some are auto-assigned (Gamescom and other expos, Addon Creator).

Others are posted on TeamSpeak’s social media accounts (instagram, facebook, twitter).

Note that most of them are only available until some date and no later than that.

Gamescom is not auto-assigned afaik.
Addon Creater is though.
Also the social media ones are mostly hidden in the pictures.

As listed on that list I posted, Gamescom 2017 onwards is a normal code. Previous expos had auto-assigned badges.

Don’t know if it’s true, but it’s listed as such.

I see