How can I fix my dual flush system?

The part that holds the flush button on the toilet has broken so the flush button falls into the tank and you need to lift the lid and fish the button out of the water to flush it - bit of a pain in the rear! I cannot find the make of the toilet or even a clue to the make anywhere and I am told that I need to know this to order a new flush. I don't know what to do next?!! I know nothing about plumbing/toilets/or any DIY for that matter!!!!