(Adds company says military units carried flag at inauguration) By Teddy Nykiel BRUSSELS, Feb 6 (Reuters) - When President Barack Obama was sworn in for his second term on Jan. 21, it's a decent bet that at least one of the flags fluttering behind him was made in Belgium. The Waelkens flag company, based in the small town of Oostrozebeke in Flanders, supplies around 2,000 flags a year to the United States, with clients including the Pentagon and other U.S. government departments as well as the United Nations.