Been googling and thinking about this because I like your idea, the DIY thought behind it, and of course, that you want to do it with a Mac. We had a photo booth thingy (provided by pros) at some friends' wedding earlier this year, and it's been a hit! So, go for it -- but...:
Probably like yourself, I found a button like the one in your link with USB, but it was only for Windows, explicitly "not for Mac". I'm sure it could still be made working on a Mac with some script, but it'll require some programming.
Possible alternative? It might sound silly and requires some fiddling, soldering, etc, but maybe this is something for you, if you haven't thought of it yourself:
- Get the large "emergency" push button you like. Watch out, most are "opening" when pushed, but you'll need one that's "closing" a circuit.
- Take an old, unused keyboard or mouse, USB or Bluetooth, Mac or Windows, see if it still works (return key, or left mouse button), take it apart to get to the contacts of return key or mouse button. You will need to solder (probably thin) wires to them, eventually also drill a hole into the housing to get them outside, and then connect them with the push button.
Whatever, good luck!