I myself very often use various decentralized exchanges to buy new coins that are not yet available on centralized exchanges.
That's interesting! Do you have an example? I was under the impression that it's easier to find liquidity of altcoins on centralized exchanges rather than decentralized exchanges (just due to the fact that they have less liquidity in general).
What example do you want to hear, because I am writing about new coins that have not yet been listed on centralized exchanges. Accordingly, such coins do not have liquidity on CEX, since they are not traded there and can only be bought on decentralized exchanges at the pre-sale stage of a public or closed round.
Do you have an example of such a decentralized exchange where these coins are sold?
And an example of such a coin?
Like: 'There is the coin X that I could only buy on exchange Y'. Simple..

Almost 90% of all coins that are present on the market can be bought only on a decentralized exchange, as this does not require the financial costs associated with listing on CEX. Accordingly, by the time of TGE, each team is listing its coin on DEX. Such an example is the Robby coin, which is traded only on Uniswap:
https://coinmarketcap.com/currencies/robby/markets/