I have just installed Laravel 5.3 and also imported the authentication package which consists of a login and registration pages.
All this works fine, my problem is: I am trying to integrate a blog, forum, newsletter system in this authentication system.
I have been searching for packages but most I have seen are packages that installed as projects.
But all I want is to integrate this component I have talked about into my existing system.
You can try and search the packages on http://packalyst.com/ or https://packagist.org for packages. You will use composer require to pull in the packages. This package looks like it might be on the track you want for the blog and this for the forum.
Those will be the best sources for packages that are not directly integrated in a Laravel project. You may also want to try a CRUD admin panel such as Voyager.
Another great find is building the blog items you need. You can find a great tutorial here that also goes over a lot of key Laravel concepts.