Accessing find-and-replace with the keyboard

In the Find dialog (cmd-F), pressing tab advances to the “replace” field, but I can’t find a keyboard command to move to any of the buttons or radio dialogs, such as the “previous” button or the “replace” button. Can these be accessed only with the mouse? If so, I would like to request that that be fixed (for accessibility reasons).

Also, just to be clear, I’ve already tried the approach recommended by Apple to access all controls on-screen with the keyboard. It doesn’t seem to work.