Where can I buy spares for my Ideal Standard dual flow cistern?

I need to replace the threaded plastic part that sits in the valve bridge or lid attachment (as I have seen it called). The part needed is used to secure the lid to the cistern. A plastic screw is passed through the dual button holder and screws into this part. Do I have to buy the whole "valve bridge"? or can the insert be bought seperately? Thanks in advance.