Here's a good workflow that will help you the next time you do a complete "Nuke and pave" of your machine. Every so often I download an app from the web not from the App Store. This process usually gives me a DMG file which lands in my downloads folder. Sometimes these files come from manufactures the don't offer a free trial so it makes it very difficult to go and download the files. Typically once you have the file you can install and then download any updates that may exist. Some manufacturers are very rigid in how you download the software especially software vendors like Microsoft and Adobe. The goal is to retain these files so that I can go back to them later when I have to reinstall them on a new machine or if I'm rebuilding an existing machine.
By setting up a folder on Dropbox called software downloads and then creating a Hazel rule, will automatically save software downloads and move them from your downloads folder. Because I store them in Dropbox they are always available whenever I need them.
I have my rule set to look for files that are older than 24 hours. You can tune that as you wish, perhaps shortening the window.
As an added step to this process I save all of my serial numbers, authentication codes, and login information to 1Password for easy retrieval later.