It is easy to find (good) markets. Just go to Coinmarket cap, search for the crypto you are interested in, and then look at the Markets tab. For example for Ripple this would be found on
https://coinmarketcap.com/currencies/ripple/#marketsAll the pairs are listed there along with the exchange, so you can find the suitable pair. If it is not listed there, then better not to use the exchange since coinmarketcap only uses exchanges which are legitimate (well, legitimate enough where trading volume can be recorded). Bithumb, Poloniex, Bittrex and Bitfinex are the biggest markets, BTC, KRW and USD.