Too small an item for them to bother with and also many cisterns are not named so it's difficult to find out who made it and if they would send the spare part. Too much of the throw away culture nowadays that's ok if you can afford it or not worried about where all the throwaway stuff is going.
If the cistern is named take note and the parts to a local plumbers merchant and you may be lucky. It may have to be ordered but flutter your eyelashes and they may take one off their stock cisterns. note name on toilet as they may be made by same firm.
Rob
March 2008