How to attach mesh (some item - ammo, objects, etc) to Mixamo rigged character via script?

I made character model in Blender and animate it via Mixamo website. I export model and animations from Mixamo, all works correctly. Character game object doesn’t contains any separated bones, it can be find only in avatar editor. This way i can’t attach items into hand. How make attach point to current bone from avatar? How to get position of current avatar bone via script? Tnx in advance for any help!

Attach the mesh as a child to the corresponding joint/bone.

//Try to instantiate it as a child of the palm

public GameObject itemPrefab;
public Transform palmLocation;

void AttachToHand()
Instantiate(itemPrefab, palmLocation);