Well, I have been wrestling with something similar off and on for several weeks. In my case installing Debian to a mid 2009 MBP. Pure is based on Debian. As you probably know, Debian concentrates on being free software only. Although some folks provide some of the other proprietary firmware “blobs” for some devices. I have read and tried a lot of suggestions as to how to get a Broadcom Wireless device to work. It is still not working. I started taking time off trying several weeks ago.
This one might work: https://www.youtube.com/watch?v=JW0f3NOjWys
This might be more helpful, near the end is what you want.
I suspect it might be interesting to ask my question of how to install the driver on Reddit or somewhere else. James Bond is a nice guy, but he, like a good techie person, is really busy.
For more amusement.
I may work on my version of the same problem this week.
I also have bought what the fellow on the Debian board suggested, I bought another laptop that is reputed to work more easily with Linux. I have work to do with getting that one working. I am hampered in that I do not have an 'At Home" internet connection, and my usual contact with the internet is at McDs, which blocks Linux, freeware downloads. My other option is our public library, which does not open again until Tuesday, and I think they are about to start restricting folks from using main power.
Keep in mind that some have said that Broadcom Internet processors do something to make it easier for the Internet Provider to watch what you do, where you go. I dunno about that.
One of my solutions is to buy a USB Linux WiFi adapter, preferably one that is pre installed in the base Linux everywhere.
Please let me know what your outcome is.