How do people find these altcoins?

Join a good discord group, The one I'm on has a trial membership and then you have to pay after. It is very worth the money. A lot of different type of investors and people with different specialties. Also start following the top 20 on Twitter, go to Coingecko.com and research the ones that have been up recently and try to figure out why. A good site for news is CCN.com.