this bits been missing for ages - there was a chrome surround for the push button thinghy. Tried the usual diy shops the only thing near was a complete replacement button and this was too small to fit this toilet. any ideas?
I'd take the whole widget out, take it to a good plumbing shop and ask 'Have you got anyhting that will replace this?' (not only functionally but that will also fit the hole in the cistern)
Who makes the cistern/ toilet? They normally come complete with the gubbins ready for install. With this in mind, I'd contact the makers/ plumbers merchant (they can source from the original manufacture).