Do you specifically need this version? If so, you can find the link to download it here. It seems there is a version for Mac.
But you can also download the latest version 2.10.0 here.
What you need to do is to unzip it and then use a terminal to use the tools in the "bin" folder inside the blast folder. I'm on Windows and that's how I do it, but it should be the same for Mac.
Here is the manual, even if I think it is not really user friendly.
Hope it will help!