You can always compose it yourself.Format:
ftp://user:password@site:port/dir_lvl1/dir_lvl2/.../file
As long as you know where your file is and what its name is, you can always compose the full URL on your own.
if using flashfxp
click on the file, then
CTRL+U
or right click on the file, choose copy URL.
CTRL+U
or right click on the file, choose copy URL.