XRP is in a strange legal place right now. But the one place I know where you can buy XRP right now if you're in the United States is Uphold.
Uphold describes itself as the place to trade "anything to anything." And while that's a pretty broad and bold statement, it is obviously a marketing campaign to attract traders, they can't possibly trade any crypto for any crypto.
They do, however, have an incredible long list of cryptocurrencies you can trade. A lot more than I see available on other big exchanges.
Check it out here: sign up with Uphold with my link here, and they'll give you $20.00 and give me $20.00; we both win. And you get to trade XRP.
There are other benefits Uphold offers, like integration with other apps and staking right in the platform.