The root of this problem is that you need to have the app in your App Store storage (you must have "bought" it) in order to get a compatible version for your OSX. But you cannot buy it because your OSX version is to low.
If by any chance you are able to borrow or log into a newer MAC, with the appropriate OS you can "purchase" the application and download it there.
Next time you open App Store on your old Mac, you will be given the option to download the last supported version of the app. Since it is registered on your account that you now own the program.
Also, having a friend with an Apple ID from which the suite has been downloaded can help. Let him log into App Store on your Mac with his ID. He can then install the program on your Mac. Afterwords you can login yourself. And the app is still yours.