Unfortunately for now there isn't.
I would have suggested to just search for "3D" but not every artist added that tag to his avatar.
But here's a list I have with the 3D avatars from the workshop:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=635416805&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=656435806&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=506920458

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=358557350

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=667724881&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=623842574&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=834600956&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=337191984

Originally posted by Aty:

Unfortunately for now there isn't.
I would have suggested to just search for "3D" but not every artist added that tag to his avatar.
But here's a list I have with the 3D avatars from the workshop:

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=635416805&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=656435806&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=506920458

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=358557350

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=667724881&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=623842574&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=834600956&searchtext=

https://steamhost.cn/steamcommunity_com/sharedfiles/filedetails/?id=337191984

whoa, thank you for taking the time to find all of them for me!

I tried to use 3D to search before I posted, and as you said, not all submissions tagged themselves with "3D."

Thanks a lot because to many of them and only somes 3D