List the sources for the Net Migration in South American countries in 2002.
South American is the name of the region; Year contains '2002'; sources refer to Description; IndicatorName = 'Net migration';
SELECT T2.Source FROM CountryNotes AS T1 INNER JOIN Series AS T2 ON T1.Seriescode = T2.SeriesCode INNER JOIN Country AS T3 ON T1.Countrycode = T3.CountryCode INNER JOIN SeriesNotes AS T4 ON T2.SeriesCode = T4.Seriescode WHERE T4.Year LIKE '%2002%' AND T2.IndicatorName = 'Net migration'