I hope this message finds you well, present circumstances excluded. I am a licensed attorney with over a decade of medico-legal experience. It is a pleasure to assist you today.
First off, I am sorry about your condition and the circumstances through which you found out about this condition. Based on what you have shared with me, it does sound like you have located the source of the test. Blood test, as you know, are performed prior to surgical procedures to test for things like Hep C.
Just because the physician left the clinic does not mean that your medical records left with him. Moreover, it is highly likely that the clinic still has copies of your medical records. I would start there by verbally requesting them and then sending a certified letter with a return receipt to the clinic requesting all of your records. They may be stored off site, but they should still have copies.
If you cannot get the records from them, then the insurance company that denied coverage may be a good secondary choice. They denied you for a reason and they may still have access to the source of that information as well.
As to filing a suit, it is possible. One issue you are going to have to overcome is the statute of limitations for filing a medical malpractice of neglect suit in one year from the occurrence. You may be able to argue that you just discovered the source of neglect and therefore the statute of limitations was tolled until you found out who diagnosed you and thus committed this act of neglect. So, you do potentially have a very viable suit, but you need to be able to overcome that affirmative defense of the defendant physician and clinic. You stand to win damages, past and future medical coverage cost damages as well as attorney fees and even punitive damages under the circumstances.
I'd start first by hammering the clinic for your records and then try to reverse the trail, so to speak, with the insurance company and how they found out this information.
Please rate my answer positively and let me know if you have any other questions or comments.