using List of records in Message Mapping

I am using SOAP - XI - RFC Structure.

(SAP CRM - .Net Application).

I need to get the list of Opportunity records.

What can I do incase I don't find a proper BAPI for getting the list of Opportunity records.

Means how can I send a request to get ListOfRecords of some entity to SAP System.

Thanks,

Narendra.