Almost all trading exchanges that exist today provide altcoin/stablecoin pairs such as usdt and busd, so I think you will be able to find stable coins on any exchange you want to use such as binance, coinbase or kucoin nowadays, I think if you have known for a long time crypto of course you will have no trouble buying a stablecoin using another altcoin or maybe deposit some fiat money to buy usdt on an exchange.