You should maintain a template which contains the master (among other things). That's going forward.
To get a master (or other layout) into a running project: Open the project with the master (A). In another AC session, open the project you want to receive the master (B). In project B, open the Organizer. On the left, open project A using the Project Chooser button. Go to the layout tab on both sides of the Organizer, then drag the master in.
If the master has drawings on it, those will become external links to project A, just so you know.
Here's another idea. You can't share the master directly, but you could do this: Create all the master data in a project file or module. Then all the real projects would have a master with that view placed as an external drawing. When/if the central view data changes, you can update the placed drawings in the projects' masters. You could also set up the template that way.
