I'm pretty active in the av1 community. Most of us who use av1 encode our own from the raw blurays or high quality remuxes. Besides the av1 content on public trackers, I think I saw a group called onlyfaffs and another one called WhiskyJack who were both putting out some av1 content, but imo, their filesizes are too large, so I avoid them if possible.

The other thing to worry about is that most people who use av1 also convert the audio to opus. Fully opensource codecs and all that. The issue is you don't know what bitrate they are using for their conversion. So audio is a concern too when downloading av1 content.

I have some guess as to why there isn't much adoption of av1 by the torrent release groups and sorry for the lack of spell check and double checking fact since it's late for me.

1. They don't care about av1.
2. Speed: it takes longer to encode a av1 video than either of the other codecs and also add the fact that they might not have GPU hardware acceleration for av1. Nvida just added it to there four thousand series.(note: I'm aware that GPU hardware acceleration give worse results than only using CPU.)
3. Limited device support. I sometimes throw a movie on a USB drive into a TV that does support anything but h264.
4. Unfamiliar with av1 so they would won't put the time and effort to find the sweet spot they like (don't fix what isn't broken). And also add the fact storage was and might be getting cheaper so av1 seems less necessary. (Note: av1 main point was to save bandwidth. My guess is pricay video streamers will enjoy it more than the torrent groups.)
5. They might dislike av1's compression artifacts. I gotten use to h264 and h265, sometimes when I watch an av1 encoded video It takes me out of the Immersion but that can be fixed with time.
6. Lack of guides. (Not entirely sure but could be a factor.)
7. Might had a previous bad experience with av1 and haven't looked back.
8. There might but less newer torrent releases group. (This seems unrelated but I have notice that they usually are the first to adopt new codecs.)

Note: I like av1 but I haven't found it outstanding for anime other than crazy low bit rates and from what I remember it is great with high resolution video which anime isn't know for.

I don't re-encode my rips but I might use it for transcoding for Jellyfin when ever set that up.

For most stuff i release, x265 objectively (vmaf and other metrics) and subjectively looks better than av1, especially for grainy stuff and older anime. I have had success only with some action movies.

Opus on the other hand... it's great

There are a handful of groups putting out what I would consider decent AV1 encodes. A couple PTs allow them, and there are groups on 1337x. Just grab a couple from each tag you can find and see if they meet your needs. Generally speaking, look for groups which note their source, which encoder they are using, and ideally what settings they used in general.

AV1 has come a long way fast, but in my experience a good x265 encode is still better for live action.

I don't mind if my server is going to have to transcode for most clients

I mean AV1 is very well supported on most clients/new devices these days. While I do not know any good groups that only encodes in AV1, I personally download high quality BD rips and re-encode them to SVT-AV1 without any visual quality loss (for my personal taste and perspective).

I'm not an audiophile or videophile and do not have the necessary devices to decode high end 1080p nor 4k video streams.

About AV1 I think only iOS devices do not have a native software/hardware AV1 decoder (I migh be wrong here).

As for your question, I wish there were more encoders that do AV1 :/

I too am interested in the answer to this question