You do not say why you have "bad blood flow". If you have major vessel occlusion in the limb, that is usually treated with surgery to bypass the occlusion.
If it is small vessel disease, such as in diabetes, there are some medicines that may be able to help.
However, if it is just in the region of the fracture, and you have been told that the bone did not heal because of poor blood supply, then in that case, you may need to have a nonunion surgery on the fractured bone.
Usually, in routine nonunions, the surgery consists of taking down the nonunion, bone grafting the defect, and stabilizing the fracture with hardware.
But, in cases where more blood supply is needed to heal the fracture, a vascularized bone graft can be done. This is where a bone is taken from somewhere else in the bone, with its blood vessel still attached. Then this piece of bone is placed in the fracture site and the blood vessels are connected to blood vessels in the region of the fracture. This requires microvascular surgery.
You need to discuss your situation with your surgeon and ask about what options you have to treat your nonunion.