What type of a physician is willing to treat chronic mod/severe back pain with opiate analgesics? Pain is intolerable, have MRI & nothing else works.

Pain Medicine. You should seek care for a fellowship trained pain medicine physician in your area.
See Pain Specialist. The only way to give you the best advice is to ask you to schedule an appt with a qualified trained pain management specialist. There are multiple treatment options but each are individual to the patient so it's hard to give basic advice here. Just an fyi, opiate analgesics are not the only option and in fact are known to make pain issues much worse in the long run.
Pain management. Opioids efficacy in acute pain such as postoperative pain is also well established. However, the use of opioids to control chronic pain is fairly recent and is a complex and controversial issue. Because of tolerance, physical dependence and addiction, many health professionals are still reluctant to prescribe opioids for chronic pain. Rec.: see a pain management specialist with opioids training.
Depends on cause . Many causes look up "dural tug" in article by gb racz in: percutaneous lysis of adhesions if pain is reproduced the simplest and best approach is caudal and transforaminal catheter lysis of adhesions. It separates the dura from posterior longitudinal ligament. Long term narcotics for a young person is not in your interest find an interventional pain doctor that is trained! gabor racz md.
Back Pain. Pain physician's will assess your pain and create a treatment plan which may or may not include opioids to help control your pain.