There are many tools that help when creating custom calendars. One easy to use tool is Calendar Templates, like the ones available at Vexels. Simply download, edit the vector template and send to print (or use digitally!).
To make a Calendar, you can download easy to edit Calendar Templates, or simply create one using any design software.
You can find tons of free 2021 Calendars on Vexels, and use them as long as they're for personal use.