Look for the ttf files here:
"Steam\steamapps\common\SCP Containment Breach Multiplayer"
And the rest of the issue is to make a mod that replaces a font file and creating a script.
You can read about the creation process of a mod here:
https://steamlists.com/scp-containment-breach-multiplayer-tutorial-guide-how-to-make-mod-in-game/
And you can find some guides right in game's guides.