I would probably start searching on Turbosquid, if you have not done that already. There are a few arm models that are fully rigged and you can specifically search for rigged models: https://www.turbosquid.com/3d-model/rigged/arms

It's hard to predict what quality these models will be, but the prices are not too steep to try them out. The most comprehensive and detailed models would probably be these https://www.turbosquid.com/3d-model/anatomy , albeit of the full human body.

Alternatively, you can use the 3rd party tool Puppet3D in Unity to rig existing models yourself. It's pretty straight-forward, even for someone without much animation/rigging experience. Unity also introduced their Animation Rigging preview package in their latest release (under Package Manager) which allows you to rig characters, including shoulders/arms/elbow/wrist/fingers.

The main questions you need to ask yourself: how realistic should the rigging be and do you need an individual arm or would a fully rigged character with a realistic arm also be acceptable.

Most rigs of characters from DAZ3D and Character Creator 3 are fully rigged, including elbows, shoulders, and individual fingers. Genesis 8 characters from DAZ have a few extra joints that give you more flexibility when animating, but you can simply lock those joints in Blender or Unity to only work with the anatomically correct joints.

Once you find the right character or separate arm model, you can either use Unity's animation/rigging system or use FinalIK or UMotion from the Assetstore to put constraints on these joints that reflect real-world anatomy.

Let me know if you have any additional questions or run into issues.

Sebastian Koenig Wow, thank you so much for all these information. :D

I already searched in turbosquid, makehumancommunity, blend swap and the Unity Assetts store and found only rigged models for the lower arm/hand or full body.

Following your links I found an whole arm model that could be suitable. :) Important for the final model is that the grades of freedom of all joints conform to the real human arm anatomy and the motion doesn't look too weird.

And it's super helpful to know about good tools which makes the rigging process easier and faster, especially for a Unity newbie like me! XD

A lots of thanks for your help :)

I am using this software: https://mb-lab-community.github.io/MB-Lab.github.io/

It is a Blender add-on.

You can create a full-human in Blender and then cut-away the body parts you don't need.

Beware. The created model doesn't constraint the rotation limits. You have to manually set them.

Luckily, the axes orientation is aligned with medical terminology (e.g., local y-axis rotation corresponds to abduction-adduction, local x-axis corresponds to flexion-extension).

Hi Fabrizio Nunnari thank you for the link. I will check out the tool. It seems pretty forward in modeling :)