there's plenty of evidence. you can start by looking into the case of Kendrick Johnston. here's a good article:

Black People Being Murdered For Their Organs

Earlier this year, 17 year old Kendrick Johnson of Georgia was found inside of a rolled up mat at Lowndes High School. Johnson’s body was upside down inside of the mat which had been placed upright behind bleachers. His internal organs were missing and the cavities were filled with newspaper. His death was ruled an accident. 24 year old Ryan Singleton of Atlanta made news just last week. His body was discovered in the desert of Death Valley by joggers. All of his organs were missing. These two stories have led to a theory that there is a black market for black organs.

Dick Gregory said in an interview, “The undertaker that dealt with Kendrick Johnson is the same undertaker from Miami that was used to deal with Trayvon Martin. You mean to tell me as close as Atlanta is, you’re going to call a black undertaker way from Florida?”

Gregory said he always felt there was something fishy about the Trayvon Martin case. “When have you seen a homicide with a emphasis on what was purchased? That’s because he never went to that store.” He believes Martin’s organs were harvested. “The biggest money maker in the country is organs,” he said.

Modern-day body snatchers provide bones, tendons and body parts other than transplantable organs to tissue banks, research facilities and other buyers. What they get paid: $600 for a brain, as much as $850 for an elbow, up to $850 for a hand, according to an analysis of market prices for fresh or frozen body parts used for research and education that was conducted by Annie Cheney, author of Body Brokers: Inside America’s Underground Trade in Human Remains.

Henrietta Lacks was an African American woman who went to Johns Hopkins Hospital in 1951 because of a painful knot in her stomach and abnormal bleeding after giving birth to her fifth child. She was diagnosed with cancer and two parts of her cervix were removed (the healthy part and the cancerous part) without her permission. The doctors discovered that Lacks cells kept alive and grew. Her cells were named HeLa and for over six decades, they have been used more 74,000 studies. HeLa were the first human cells to be successfully cloned.

Back in 2006, USA Today wrote an article about the trafficking of illegally harvested body parts and tissue from the dead. At the time of the article, more than 16,000 families had been represented in lawsuits claiming that their loved ones body parts had been stolen.

In 2008, a former New Jersey dentist named Michael Mastromarino was sentenced to 18-54 years in prison after he made millions from selling human organs and tissue. According to reports, he secretly robbed thousands of corpses from funeral homes in New York, New Jersey and Philadelphia. He never screened the parts for disease and he doctored paper work to change the age and cause of death. He died from bone and brain cancer in July.