Does a device such as an inverse triac exist?
Does anyone know of a device that would do such a job?


You can use a low resource micro-controller, and if you decide to add functions, on some cases you could simple rewrite the firmware.

You can do this with logic circuits too. Where is an example:


Copyright http://www.next.gr

There are more simple circuits, the idea is to block the others inputs when one is pressed.

In this specific circuit, when one input goes low (a key is pressed), the output goes low to, lighting the led. Also the outputs are connected via NAND ports to the Enable pin of the latch. So when one output goes low, the latch is not more enabled until reset is pressed. The resistors (except for the ones with the leds that are current limiters) are pull-ups for the pushbuttons.