To see what reddit avatars are still available, new, you have a few options
1. Go to https://www.redditavatars.io/ this is a website that allows you to see how many of each Reddit Avatar are still available.
2. Open Reddit.com, click on your username in the upper right corner, then click "Style Avatar" you should see collectible Avatars, and you can see which Avatars are still available for purchase
3. Open Reddit on your mobile phone, tap on your avatar in the upper right of the screen, then click your avatar in the middle of the screen, and you should see collectible Avatars, and you can see which Avatars are still available for purchase.
Once Reddit sells out of Collectible Avatars, you will need to purchase them on the secondary markets like OpenSea.io