If I have a bunch of records that need to be fetched together often and can't be dumped in a hstore of JSON column, how can I ensure data locality on disk in po

If I have a bunch of records that need to be fetched together often and can't be dumped in a hstore of JSON column, how can I ensure data locality on disk in postgres? Since primary key is clustered in MySQL, I choose an appropriate key. Is there an equivalent mechanism or is periodically running the cluster command the only option?