Indeed, there is no menu option currently to show the Resource Calendar for a Group. A feature request already exists, and I have voted for it on your behalf.
As you may have already discovered, in the Resources subsystem, you can add the "User.Member of" column/field to your view (by clicking the "Columns" dropdown) to show what group(s) a resource belongs to. Then, you can click on the column header for this property (entitled "Member of"), select "Is..." and enter the name of the group you are looking for. All individuals that belong to this specific group will be shown (even if they belong to other groups).
I hope this clarifies!