The founding of the Theosophical Society and initiation of the I AM Activities preceded the giving of the Ascended Master teachings.
I Am Activities:
Who are the Ascended Masters?
There are other organizations that provide access to the Teachings of the Ascended Masters, but their information is not entirely up to date. This said, however, they’ve had many years to organize their material and can provide (perhaps even ‘overly extensive’) exposure to Ascended Master Teachings.
Supplementing and grounding the above organizations is the Ascension-Research site: