I made a custom Border Collie model for VRChat from scratch. It's pretty rough, but works well enough and I learned a lot in the process. (I have fixed the seams since this screenshot was taken.) This model is very efficient, about 5000 triangles and only one shader. It contains bones in the ears and tail which can be jiggle bones in VRChat.
It exists in VRChat but there's no easy way to find it (I didn't put it in any avatar worlds).
Here is the blender file: http://collies.xyz/BorderCollieV5.zip
This file is released under the Creative Commons Attribution-NonCommercial 4.0 International license.
Thanks to  Nyaasu and  Raaz for references.