Where would a surgeon take a bone graft from to attach to the ulna bone to fix a bone length difference?

Bone graft : Can be autologous. From the same person Or an allograft. From a different person or a bone graft substitute can be used. Common sites for autologous grafts are the pelvis, the distal radius , ribs and the fibula. Allografts or donated bone can be from these sites too but also come in smaller pieces. A lot depends upon the procedure , the length needed, the general health and why it's done