Those holders/switches could have been out of almost anything. They look similar to Gottlieb flipper button leafs, and to stuff I have seen in early 80s Sega cabinets. But, they really could be from ANYTHING.
My own personal suggestion is to build the panel out of some fairly thick (like 3/4" wood), there are solid state arcade buttons out there that could reside completely within the hole you drilled for the button, with just a couple of wires poking out (so no clearance issues).
I have a few of them, 4 of them installed on my Do! Run Run cabinet, and a few more in the parts box. I am unsure of their original source though, and they DO NOT look the same as a standard leaf or micro button (bezel part is tiny, while the "button" part is larger and flat).