Dan,
You can take a look at this national
list of basketball organizations that includes identification of interpreters and some email addresses. Please share any additions with me so that I can update the list. Also, do share the results of your survey of interpreters.
I am the rules interpreter for a Philadelphia PIAA chapter. Most Pennsylvania chapters, including mine, are not IAABO affiliated. Here are 2 positives and one negative regarding PIAA rules related matters.
Positive 1:
Each year, the PIAA provides a detailed guide for suggested rules presentations at chapter meetings.
Positive 2;
During the annual PIAA officials convention, the PIAA runs a full 2-day train the trainer course which focuses on effective rules presentations. Officials from multiple sports attend providing a learning experience in itself.
Negative 1: The PIAA does not require an official to participate in a rules course before taking the NFHS exam. The immediate downside is a high failure rate (around 50%). The longer term downside is that many officials miss an initial opportunity to become well grounded in the rules.
Score one for IAABO. I am also an IAABO member and have found their training for cadets (new officials) to be consistently effective and their camps for newer officials to be outstanding and true to the letter and spirit of NFHS rules.