If you still have the base part take it to a local plumbing shop/showroom and see if they have any cistern matching the flush and bolt securing holes or take a paper template of the hole positions lay paper over the holes pierce with pencil roughly hole centres. Or I've looked on web and although B&Q show out of stock in store they seem to have suites on home delivery so plead with them to supply you with a cistern only
BB
February 2010