Once the file is downloaded to your hard disk, it's totally detached from where it came from. So looking at it doesn't help to find that out in any way.

Things you can try:
1. Look in your browser history what sites you visited on the day you downloaded that mp3 file.
2. Search (with Bing or Google) for something like DOWNLOAD "WITH YOU" "MATT SIMONS" (titel and artist in quotes if they contain spaces)
3. Search for the filename of the file you downloaded like "with you.mp3".

Since you write that you already did #2 and #3, #1 is the only option left.