The Acquisition Program (and Acquisition Date) is set automatically by Marketo when a new lead is created as a result of a Marketo program. For those leads that were created before you implemented Marketo programs, you can export a list from Marketo that has the SFDC Campaigns column, but it includes all the campaigns they are a member of, not just the first one. You may be able to use fields like Original Referrer, Original Search Engine, Original Source Type, Registration Source type and Registration Source Info to help identify the lead source. Another possibility is to export your leads with their SFDC ID and creation date, export the campaign member reports with their SFDC Lead / Contact ID, campaign name/ID and campaign member response date and then use Excel's VLOOKUP to cross-reference where the campaign member response date and the creation date match.