How to query transfers for single source to single destination?
I don't know all of your source data (or why there isn't any type of unique constraint that would prevent full-on duplicates or a source with multiple destinations), but given only the sample data supplied:

;WITH s AS 
(
  -- first let's eliminate duplicates
  SELECT DISTINCT Source, Destination 
    FROM dbo.MyTable
)
SELECT Source, Destination
FROM s
WHERE NOT EXISTS
(
  SELECT 1 FROM s AS d WHERE 

  -- eliminate chains in either direction:
    d.Destination = s.Source OR d.Source = s.Destination

  -- eliminate any source with multiple destinations:
    OR (d.Source = s.Source AND d.Destination &lt;&gt; s.Destination)

  -- eliminate any destination with more than one source
    OR (d.Destination = s.Destination AND d.Source &lt;&gt; s.Source)
);


SQL fiddle demo