> but none of them are linked to from anywhere. is this 
> possible

No - the HTTP protocol does not normally allows to "list" a 
folder ; sometimes you can "see" folder listings, but this 
is generally due to a lack of default page (index.html or 
index.php, for example)

You can try to extract urls from the flash file, using 
something like (unix-bash script, or cygwin script)
cat myfile.swf | strings | grep "http://" | sort -u

But I can't guarantee that it will work, especially if the 
flash file is compressed..