For listing in big exchanges, usually trader community will discuss, or maybe started with coins that sent to exchange's wallet. I think something like that not very hard to get because some trading group or maybe trading signal channel. Mostly we can find it in telegram.
There are a lot of Telegram groups discussing new coins right now and I'm also following them to get the latest information.
Telegram is the best place to find the latest crypto information and Twitter is also a social media that talks a lot about cryptocurrencies.
Rumors about listing new coins on major exchanges will continue to circulate in various groups.