The IMF still charges for many of its data bases, although free trial periods are available for some. It does make its World Economic Outlook publication and a summary of data freely available at http://www.imf.org/external/pubs/ft/weo/2013/01/weodata/index.aspx.
The fields in the IMF_LU table are:
IMFCountryLC: The IMF spelling of the country name.
ISOCountryLC: The ISO spelling of the country name.
ISO3A: The ISO three character country code.
IMF3N: The three digit World Economic Outlook country code.
The chart below shows the first few rows of the look-up table.
To download the IMF_LU lookup table which is in Excel (.xls) format click here.