Because of difficulties in supporting shortcut keys in certain development environments, this feature was not included in 3.0. I would expect to see it in a future version of TestStand.
In the meantime, you could:
a) Create a menu item that is bound to the same command as the button. The menu item will handle the shortcut key.
b) Look for the missing shortcut keys yourself via CVI callbacks or underlying winprocs.
c) Use a CVI button. You can still use the corresponding Command object to implement the command, determine its label, etc.