I don’t know if the Town of Leesburg ever had a flag but, Loudon County does. Here is the history and description of the flag:
http://www.loudoun.gov/Default.aspx?tabid=505
http://www.loudoun.gov/Default.aspx?tabid=553
And an image of the flag, by our own, Joe McMillan can be found here:
http://www.fotw.us/Flags/us-valdn.html
Here is the seal:
http://www.loudoun.gov/Default.aspx?tabid=516
I remember seeing the coat of arms with supporters and crest. I will have to look through my books and scan it.