I can get NBC Sports Gold app on my living room TV but not my bedroom TV. Perhaps b/c my bedroom TV is my "additional outlet", and it also doesn't have a DVR box, just a regular box (although I can watch DVR recordings on it)? Oh well, happy to watch on TV vs my laptop.
I have a similar problem with both of my newer TVs now (older Roku allowed me to install the app), but there is a workaround as long as it's a smart TV (or at least should work..). Open the Sports Gold app on your phone, and as long as you are connected to the same wireless network on both the phone and the TV, you should be able to cast to your TV. Of course it depends on the TV, but I'd imagine most of the newer ones-- anything really since smart TVs became a thing-- should allow you to do this.
PS- the TV outlet stuff has nothing to do with it. Either the TV is set up to allow you to install from a huge library of apps (where you would find Sports Gold), or they only permit certain ones that can be installed/used. My old TV was the former, my new 75" is the latter.
Another note- you don't have to have your phone screen on the app while it's being cast to the TV. You can text, browse the web, whatever else you typically would do. It will use your battery faster, but not as a severe rate. If you're home, you can be charging it anyways.
If any of you are having trouble with my explanation or need further details, feel free to PM me.