Buzzer Commander is a simple WinForms and C# buzzer program that let's two contestants face-off against each other to see who can ring-in first. It does lockout once someone rings in and resets itself after 5 seconds. I built it for a Family Feud-style game night we held.
The buzzers were built using standard arcade buttons, hooked up to a USB joystick encoder card. Both can be found on Amazon pretty inexpensively. The SharpDX library was used to listen for button activations.
The program listens for joystick buttons 11 and 12, which I've referred to as Buzzer A and Buzzer B, respectively (note: SharpDX refers to them as buttons 10 and 11, since they start with button 0). Anyway, there's certainly tons of room for improvement, but hopefully this will be a good starting point for your project.