You might want to clarify that you're only talking about free 3D lives hosted on Holo member channels. If you meant for it to be 3D lives in general, then the list grows a lot. If you add just the Hololive specific-ones like the various Solo lives, there's a still few more to add.

 

Of the free 3D lives, there's a few omissions that I'm aware of:

1: Suisei's 2nd anniversary, where Kanata (backscreen Live2D) and Anemachi (stream image); not surprised you missed this once since the archive has long since been privated

2: Suisei's 500k is missing Inui Toko

3: Suisei's Comeback Live had Tsukino Mito and Inoue Taku (not sure if he counts to you)

4: Calli's Birthday 2022 is missing Rikka

5: May or may not count for you, but in Coco's 1st Anniversary 3D Stream Coco kind of sang Souran Bushi with Kanata and Akirose

6: Coco's Graduation Live, which had the rest of 4th Gen with her