Macau pass is not (officially) available in Hong Kong - I cannot find any posts from local forums saying it is sold in any outlets in Hong Kong (not even the Hong Kong - Macau Ferry Port in Sheung Wan). This means the OP can only purchase a Macau Pass once they reach Macau (i.e., after taking the Hong Kong - Zhuhai - Macau Bridge shuttle bus).
This is unlikely an issue to the OP as Macau Pass is not accepted for payment at the HZMB Hong Kong Port anyway, according to the operator (Chinese only). It is accepted at the Macau Port for the shuttle buses travelling the other way, though. The OP may consider paying for the shuttle bus ticket using, e.g., HKD/MOP/RMB cash, (Hong Kong) Octopus, Visa/Mastercard (debit or credit), WeChat Pay, or AliPay.
Given the OP's route, the earliest point where one can buy a Macau Pass is a convenience store at the arrival level in the HZMB Macau Port (G/F, Unit C115 from this document hosted by Macau Pass (entry 2315)). The store and the surrounding area looks like this or this in July 2023. It does mark up the price (MOP 140 cash / MOP 145 card payment for a card with, officially, MOP 100 balance and MOP 30 card fee). I am not affiliated with the store or the youtube channels.
The OP may also consider getting a Macau Pass from any of the outlets listed on the Macau Pass website, with the official price of MOP 130, once they reach the urban area in Macau. It is the "best" in terms of price, though it comes with the inconvenience of sourcing MOP cash for the bus or taxi ride into town.
Aside: There are many local buses that go between Hong Kong International Airport and HZMB Hong Kong Port. Most of them are Airport buses that are bound for Hong Kong city centre and are priced accordingly. The most economical option would be Bus B4, operated by New Lantao Bus (HKD 9.1).