unfortunately post-fix statements cant be nested w/o do-blocks.

I'd suggest:

print "$_ could not be restored!\n" 
    for grep { not exists $found{$_} } 
        @files;
[download]

or even

print 
    map {"$_ could not be restored!\n" } 
        grep { not exists $found{$_} } 
            @files;
[download]