Money – Where can I get MOP coins in Hong Kong?

Bus drivers in Macau do not accept Octopus / credit / debit card, do not return any changes, and bus tickets generally cost 6 MOP. In addition, if paid with HKD, the exchange rate is disadvantageous (1 HKD = 1 MOP instead of 1 HKD = 1.03 MOP). Therefore, one must pay for bus trips in MOP currencies if one does not wish to overpay (unless you have a Macao bus card).

Where can I get MOP coins in Hong Kong?