Where to download already installed game on xbox 360 HDD

I have 2 owned COD Black ops 2 disks, but i am unable to install to XBOX 360 HDD as is stops at 60% and gives an error. to download it from XBOX store I will need to pay since I have not purchased it online but own the original disc, How can I go about the download? If I had a friend with the game installed on there HDD I could have just copied it from there but I don’t.