Can't Get Garageband 5.1

So community, I wrote some music on an iMac using garageband 5.1. I have a new MacPro and it has garageband 10.10 or something. It's not able to play the original garageband files so I need to download version 5.1. When I google it, I keep getting .dng files which don't seem to do anything. Is there anywhere I can go that just lets me download version 5.1 to my Mac Pro?