Vaad Arba Aratzos as source for the minhag is brought in Mishna Halochos Chelek 12, siman 95. As a historical aside the Vaad handled all communal matters, including takonos for religious standards. It was run by rabbonim, not askonim.
Source in Zohar to shave after yemei niddah is Parshas Achrei Mos, (chelek Gimel) daf 79a. It is very clearly mashma that this refers to shaving the head to bald. How the Ari says in Shaar HaMitzvos seems to be a stirah with this part of the Zohar, but if you look inside it’s very clear.