As of now, Coinbase does not offer the ability to buy moonriver directly. However, there are a few workaround methods that may be of use to you.
The first option is to use Coinbase’s built-in GDAX exchange to buy Ethereum or Litecoin, and then transfer those funds to an exchange that does offer moonriver trading. Binance is a popular choice for this, as it offers a wide variety of altcoins to trade.
Another option is to use a service like Changelly or Shapeshift, which allows you to directly convert your fiat currency into moonriver. These services typically charge a higher fee than exchanges, but can be convenient if you don’t want to go through the hassle of setting up an account on an exchange.
Ultimately, whether or not you can buy moonriver on Coinbase will depend on how the cryptocurrency is trading on other exchanges. If there is enough demand, it’s possible that Coinbase will eventually add moonriver to its platform.