I would like to add the viewport command to one of my toolbars.  When I try to customize, there is no viewport command in the customization files.  (It is available in Options/User Preferences/Aliases.)

I can add a new command but to do that I must know the command string and select icons.  I'm sure I can find appropriate icons.  Perhaps there are even unused icons in Icon Explorer.  I certainly don't know the correct command string.

Can anyone tell me the command string and/or point out any unused icons?