I made an Illustrator script that generates a calendar grid. I know there are many. But mine is the best.
Styles are defined for all day types (weekdays, weekends, etc.) and can be customized. If you do not need days from adjacent months, set their style to no fill and they disappear.
The grid scales correctly to any format. Enjoy — a like is appreciated.
P.S. Download the script to any folder and run it via File » Scripts » Other Script…, then select the saved file.
Run it in a new document so you do not break the current file.
