Some privacy coins are banned from exchanges. When buying privacy coins that have been delisted/banned from exchanges it’s best to buy them from a decentralised exchange (DEX). One of the most popular DEX’s is Uniswap.
To buy from Uniswap you will need a non-custodial crypto wallet like Metamask or Trustwallet, and own some Ethereum inside it. Once you’ve connected your wallet to Uniswap simply search for the privacy coin using its address or name, then purchase the number of coins that you want. Those coins can then be kept in your wallet.