I regularly check the current information of altcoins on coinmarketcap. Another way to do is by joining some telegram channels that inform current improvement on altcoins. I think the two ways are enough to have the updates of new altcoins.
There's another way of knowing about these newest altcoins and projects with the specific sections of the forum.
There is these two sections,
Announcements (Altcoins) and
Tokens (Altcoins) and if their ann threads has lesser page, there's a chance that those projects are new but it's not like that all of the time.