AppleScript to Make New Calendar in Specific Account
You could use GUI scripting like this...

tell application "System Events"
    click menu item "iCloud" of menu 1 of menu item ¬
        "New Calendar " of menu 1 of menu bar item ¬
        "File" of menu bar 1 of application process "Calendar"
end tell


But one of the problems with this solution is you cannot set the properties of the calendar.  The new calendar will be named "Untitled"