You’re not just limited to installing Ansible roles from Ansible Galaxy, you can use public and private git repos too.

Here I’m installing Oefenweb’s Dropbox role using the git+https syntax for a publicly accessible git url:

ansible-galaxy install --roles-path ./roles https://github.com/Oefenweb/ansible-dropbox.git

And here, I’m accessing Foo’s private weevils repository that I have access to (using the git+git syntax):

ansible-galaxy install --roles-path ./roles git+git://example.com/foo/weevils.git

As well as adding these individually from the commandline, you could add them to a requirements.txt file which you could then use all the roles to install with ansible-galaxy install -r requirements.yml.