How do I get one?

You have to create it. It's dead easy, just follow these steps.

• Open the folder X:\Program Files\Steam\SteamApps\common\Counter-Strike Global Offensive\csgo\cfg (where 'X' is the drive you have Steam installing it's games to - probably 'C').
• Right-click it and create a new text file called autoexec.cfg
• Open the new file in a text editor like Notepad (not Word!).
• Paste your config into the new file.
• Save and close.
• Now, to make sure it loads at the right time, open up config.cfg in Notepad
• Add exec autoexec.cfg at the bottom.
• Save and close.
• You're done! Fire up CS and see.