How to add more "show as" colors options in outlook?

Hello to you all,
I'm working in a company that has few sites around the country,
All the branches use the same Exchange server.

The problem is when you want to schedule a meeting with someone you can't
know if he can attend the meeting or not.

When you schedule a meeting you can choose "Busy", "Free" or "Out of office"
– so if you work in branch "A" you use the "Busy" marking for a meeting in
your own office and for every meeting out of branch "A" you use the "Out of
office" marking.

The problem is how can you know if someone is in a meeting in branch "B" of
"C" or with a client someplace out of the office? Everything is marked the
same (out of office).

Is there a way to add more markings to the "show as" option in the calendar
so you can mark each branch with different color?

In that way you can always know if you can s schedule a meeting with someone
based on where he is.

Any ideas how to do it?

Thanks,
Ram