My 82 Year Old Father Has Bladder Cancer On The

My 82 year old father has Bladder cancer on the lung. He had his bladder removed 3 and a half years ago.
He started chemo 3 months later. After chemo they did a scan and found that the bladder cancer had spread to his lungs. He got on a trial immunotherapy drip every 3 weeks and was on that program for 2 years. During that time his cat scan came back showing reduced shrinkage of the 2 small tumors on his lung. A few months later there was no detectable tumors. However this past summer the immunotherapy drug he was on quit working, the cancer was back on his lungs and he was kicked off the trial.
Now, he found a doctor that took tissue from his original bladder cancer removal and did a gene match to see if they had any drugs that would help him. They have a definitive genetic mutation match for my Dad. The doctors said that they,ve had 80% success rate using Gilotrif with the specific genetic mutation that my Dad has. Here's the problem. Medicare approved it, my Dad's supplemental insurance won't help pay any of his co pay for the prescription. Who can we go to for some help in getting part or all of his co pay covered? I would think the pharma company would want people to take their drug if it is go great and sounds 100% better than chemo and radiation. Any help or guidance in the right direction would be a great burden off my Dad's mind and much appreciated. Any suggestions??