Who is my husbands father and how can I find out?

My husband does not know who his father is.

I know there are plenty of people who will read that first sentence and shrug their shoulders and say "So what, I don't know who my father is either!"
This is the story: (and maybe someone can send me in the right direction or tell me where to start)
My husband Eric was born in Chattanooga, Tennessee in 1969. Eric was born to a mother who loved him, no doubt, but who couldn't take care of him properly. I guess that in those days, women needed to know who the father of their children were or they were looked down upon. When Eric was born, he looked almost Caucasian. He had dirty blond hair, very light skin, thin lips, and light brown eyes. His birth mom, Thelma was light skinned but obviously African American. A lot of the blacks in his neighborhood speculated that Eric's father was a white man because of Eric's appearance. People today still ask if I married a white man when they meet him. However, the name on Eric's birth certificate belonged to a very dark, black man with strong African American features and Eric was named after him.

At age 2, Thelma gave Eric up for adoption. He was adopted by his much older cousin and her husband and they relocated to Florida in 1971. For years, Eric believed that he at least knew who his father was although he had no relationship with this man. In 1989, this man was shot and killed in California. I met Eric a few years later and he has always expressed interest in finding the family of his father. I recently began searching for these people because Thelma refused to give him any vital information to assist with finding them. She passed away taking this information to her grave.
In my search, I came across a woman still living in California named Evelyn who was either in a long term relationship with the man my husband called his father or they were married. Evelyn knew of my husband but at first, refused to talk to me. After calling her a few times, she finally agreed to talk to me and she gave me some very vital information. She told me that the man who signed my husbands birth certificate, Eric Jones Sr., was not his father but just a man who had possibly had a relationship (maybe only sexual) with Thelma. Evelyn also told me that she was originally from Chattanooga, Tennessee and that she knew Thelma very well. Years ago, Evelyn and Thelma were enemies because of the relationship they shared with Eric Jones Sr. Evelyn referred to Thelma as "a lady of the night" which I later understood to mean that she was saying Thelma was a prostitute. Evelyn stated that Mr. Eric Jones had signed my husband Eric's birth certificate out of sympathy. He felt attached to my husband at the time and therefore agreed to step in as his father. He later regretted this decision and moved on with his life without ever getting to know my husband. That wasn't the most important thing she told me though. She happened to mention that there was an older Caucasian gentleman who frequented this small black neighborhood looking for prostitutes. She says that she didn't know his name but everyone in the neighborhood speculated that he was Eric's biological father. My heart broke for my husband. So now it seems that my husband was actually born through prostitution which means the odds of finding his father, without a first and last name, are probably very slim. It's been about a year since I devastated Eric with this information and I haven't done anymore research because I've pretty much hit a brick wall figuratively and mentally!
My husband is the best man I've ever met. He was raised by adoptive parents who loves him very much and raised him to be a fantastic person and a wonderful man. He's sweet, sincere, very responsible, takes care of home, always thinks on his feet, has a heart of gold, and cares for me deeply. His adoptive parents, who are Christians, know nothing about his biological mother's lifestyle. Many of you may ask why he even wants to know who this man is and especially under these circumstances. It's not my position to question or judge why a man feels the need to know his father but if it's important to him, then it's important to me and although I don't expect it to be important to you, I am only seeking advice or direction. I feel that as his wife, and someone who loves him unconditionally, I will spend the rest of my life, if necessary, searching for his biological father or at least his identity because I feel he at least deserves to know his true bloodlines. Not to mention, Eric and I carry the last name of a man who signed his birth certificate out of sympathy!

My reason for this blog is because I can't get past this brick wall. Where can I go from here? No name, No anything! Do I stand a chance at finding him?