The easy way to do this is to make the buttons the children of a
`canvas` widget, place them in the canvas with `canvas create window
...` and attach a `scrollbar` to the canvas.  For example:

scrollbar .sy -orient v -command ".c yview"
canvas .c -yscrollcommand ".sy set"
pack .sy -fill y -side right
pack .c -fill both -expand 1 -side left
set x 2
set y 2
for {set i 0} {$i<20} {incr i} {
    button .c.b$i -text [list Button $i] -width 10 -command [list puts "$i pressed"]
    .c create window $x $y -window .c.b$i -anchor nw
    incr y [winfo reqheight .c.b$i]
}
.c configure -scrollregion [list 0 0 [winfo reqwidth .c.b0] $y]  -width [winfo reqwidth .c.b0]