Unfortunately this isn't possible. You can only have 1 Outlook icon on the taskbar. When you have the Calendar open in a new window, it will just group that page behind the Outlook icon that is already present. There is not any way to pin that to the taskbar.

Actually it is possible, but it's just not pretty. I was hoping to find something straightforward. Instead I have now achieved it through a batch file.

1. create batchfile in notepad which executes "outlook /select outlook:calendar"
2. pin "cmd.exe" to taskbar
3. edit properties of newly added taskbar link
4. change the taskbar link so that it runs "%windir%\system32\cmd.exe /C BATCHFILENAME.bat"
5. change the icon to reflect something calendar-like

And it works.

It would be nice if there were an option to make your own taskbar links where you could just have it execute "run" commands. If you go to "run" (by pressing windows+r) and type "outlook /select outlook:calendar" it actually does what I want. It would be really nice if I could do this straight from the taskbar (not using a batchfile in between)

If someone figures out how, please let me know.