At the moment Oasis City is not yet listed on Coinmarketcap but it is planned in the near future.
Alternative to Coinmarketcap is CoinGecko where OSC is listed: https://www.coingecko.com/en/coins/oasis-city

Currently you can buy OSC only at Hotbit with 2 trading pairs:
BTC: https://www.hotbit.io/exchange?symbol=OSC_BTC
USDT: https://www.hotbit.io/exchange?symbol=OSC_USDT