They're not available quite yet; they're waiting for the next site-wide update to go live, which should hopefully be very soon! When they are ready, you'll be able to find them on the second page of the mood theme preview page; mine will be called Socchan's Fancy Rats (featuring rats like in my icon here, and I have them uploaded as my own custom mood theme here*) and Socchan's [color] Jellyfish (you can see a basic preview here). I've been super excited for them to be available ever since I found out that they were going to be official mood themes, so a little more waiting probably won't kill me 😂

* Technically there are a couple that are a little different from the final, site-supported version, since Dreamwidth can't use the fanart ones; but if you like them, you're good to use them as icons!