One can find the list of top 300 crypto exchanges from https://coinmarketcap.com/rankings/exchanges/. Of course it might be hard to get the popular exchange names.
For example binance.eth is already registered 22nd June 2017. But BinanceJEX for Binance Japan is still available. However be warned that Binance is supposely not support to have operations in Japan.
Similarly, Lykke is a swiss based cryptoexchange (ranked #82 and still has its full name "lykkeexchange" available). "Lykke" is even more interesting. It has not been renewed and it going to be set to be buyable on 2022.02.25 at 18:13 (UTC+08:00)
Crypto exchanges can also use permutations of names like for Lykke Exchange, the following might be useful: LykkeExchange, LykkeEx, LykkeExchng. Thought the most useful will be Lykke.
Overall there are still many opportunities in Crypto exhcnage names worth looking into.