How to check for a specific block in the world and activate a procedure

Hi,

So, I'm trying to make an explosives mod, and I have a main explosive that will be used as a sort of activation bomb, but what I want is a "remote" detonator, so basically, you right click the remote, and it opens a GUI which gives a button, allowing you to detonate the main explosive. How do I go about doing this?

So far, I have a GUI and the items created, but I have no idea how to make it, when pressing the button, look for the main explosive within the world, so not in a specific location, throughout the world (not sure if that's possible) and cause that block to explode.

Thanks,

Dan