I haven't seen anybody selling those; I think they went extinct along with 2-d, no ending, non-scrolling games. 
I'd troll ebay for "control panel" if I was you.
I'll have you know that leafswitch buttons are alive and well thank you very much. 
Arcade Shop Amusements
Centsible Amusements
Arcade Games.Com
Bob Roberts
Wico
Suzo
Marco Specialties Inc. All sell leafswitch pushbuttons in translucent and opaque colors. About half of them sell both short and long styles.
You're missing the point. Leaf-switch buttons are easy to find, yes. They are concave, yes. They are a bit deeper than the ones Happ sells for microswitches, yes.
But I was referring to the specific buttons koolmoecraig was looking for. If you find an arcade with some really old machines in it, that haven't had all their parts replaced, you might find some with different buttons, as once upon a time, there were other manufacturers, with different molds. Some of them had deeper concavities than the ones sold at the places you listed. They stuck up higher above the lip of the button assembly, as well.
Doesn't anybody besides koolmoecraig and I remember these?