If you can’t find a LinkedIn group that matches your needs, just create one of your own! It’s a fairly easy process and one where most of the work is actually done before you even create the group within LinkedIn.
One of the first things you need to do is describe the group’s mission or purpose, your goals for the group, and then consider deciding on a code of conduct as well. As an example, for my Bella Domain Networking group one of my “rules” is: Be nice or leave. You might also want to include things like what your policy will be if members post things that aren’t relevant to the group, start contacting members with direct solicitations or are just way “off topic” in general.
When you’re ready to create and promote the group you can even upload a logo/icon for it (caution: there is a max. on the number of times you can change the image), and if set up correctly, any group can be super easy to manage and moderate. For some inspiration, please feel free to check out the group I launched last year called Bella Domain Networking.