A few tool windows include access to their toolbars in their tab order (so you can press Tab and reach it), like the Properties Window, but most do not.  Most of our tool windows use the MSOCommandBars for the toolbars which don’t allow you to tab to them. 

To reach these toolbars, press Left Shift+Alt.  (The order in which you press and hold the keys matters).

Happy Visual Studio’ing!