Refer http://docs.splunk.com/Documentation/Splunk/6.1/Indexer/Removeextrabucketcopies, this documentation provide the list of excess buckets using command
splunk list excess-buckets [index-name]
This just provide the count of excess bucket but not bucket id's
To get the list of excess replicated Buckets you can run the following search on the Cluster Master
|rest /services/cluster/master/buckets filter=replication_count>
To get the list of excess search buckets you can run the following search on the Cluster Master
|rest /services/cluster/master/buckets filter=search_count>