OTC platforms/providers/brokers are over-the-counter agents who connect buyers and sellers in the marketplace, charging a commission fee. Such platforms mainly target large investors that use the services of trusted brokers and intermediaries. Although some OTC providers publish reports on their portfolios, it is almost impossible to assess their trading volume.
One can also buy cryptocurrency in bulk on the traditional centralized exchanges, but there are two significant shortcomings. First, the required amount of cryptocurrency may be unavailable. Second, while the order will be being filled, the coin will start rising in price. There are no fixed prices in such trades.