Where do banks buy gold coins?

Could you elaborate on the typical avenues banks utilize to acquire gold coins? Are there specific marketplaces or auctions they tend to frequent? Do they have direct relationships with mints or are they more likely to purchase through brokers? Additionally, are there any regulatory considerations that banks must take into account before making such investments? Understanding the entire process of how banks source and acquire gold coins would provide valuable insights into the current financial and commodity market landscape.