I’m not sure if it was the Avesta community that discouraged conversions but it seemed quite cut and dried. I agree with you on the no original members at the beginning thing!
The Avesta community is headed by a Parsi Zoroastrian and most members are Parsis too. Yes, unfortunately they can be quite dogmatic.
In the U.S. there is the Federation of Zoroastrian Associations of North America. There are other Z associations and communities in U.S. and Canada too. You’ll find their views are much less dogmatic.