The best way you can filter all of the adult games on the site is to:
-Click on Games
-Scroll down until you see "High Ranking Classics"
-Click the option next to it that says "Best of the Ages"
-You will now see Ratings after "Range" and "Sort By". Since you only want to view the adult games, Click on the E, T, and M icons so that they're crossed out. If the A is crossed out, too, which it usually is, just click it, so it's no longer crossed out.
-This will make it so you can go through all of the A rated games on Newgrounds.
Also, in your settings, you can set it so Adult rated content will play automatically instead of getting a Warning: Adult Content prompt every time.
Hope this helped.