Dad Beating Cancer- Medical Bills

Dad was diagnosed unexpectedly with stage 4 cancer in December, right after we moved him to California. He has cancer in his colon, liver, and kidney and has just started his 5th round of chemo. His cancer in his liver has grown and now must undergo a stronger chemo. We need it to shrink so he can do other treatment such as surgery or radiation.
Do to his age (90 years young ) and pre existing medical conditions, he is unable to get secondary insurance. Medicare will only cover 80% of his bills, leaving us with the remaining 20%. Bills are adding up and we would appreciate any help. You all have been so amazing checking up on dad and praying for him. Please keep it up We appreciate you all so much.  He’s such a fighter and so strong! I will keep you all updated on his treatment and progress. Love you all!