Furniture made of elephant skins and hippo skulls, paintings on ears ripped from dead elephants and belts made of stingray skins were being sold at the annual celebration in Nevada of wildlife trophy-hunting.
The undercover investigators have reported their findings to the authorities, asking them to prosecute.
The 2019 Safari Club International (SCI) convention, held last week, is organised for hunters who kill wildlife worldwide for their heads, hides, teeth and bones.
The investigators from Humane Society International (HSI) said they found more than a dozen stallholders selling apparently illegal products, including:
Paintings on elephant ears and skins
An elephant skin bench
Elephant leather boots, belts, and saddles
An entire mammoth tusk
Stingray skin boots, shoes, belts and purses
Hippo hide belts and boots
Shark skin belts
A narwhal tusk handle knife
They were also offered “canned” lion hunts, in which buyers may shoot an African lion bred in captivity for the sole purpose of being shot in an enclosed area.
SCI said it does not allow such hunts to be sold at conventions but vendors showed investigators sample pictures of lions to kill, priced according to age, size and mane.
One told the undercover investigators he and his children had killed a lion within 90 minutes. Another offered to order an especially large lion to kill.
Kitty Block, president of HSI, said: “Seeing these wild animals reduced to nothing more than useless items is grotesque.
“The world’s leading trophy-hunting industry group is apparently promoting, enabling, and profiting from the illegal wildlife trade and unethical hunting practices.
“Conservation laws and hunting ethics are thrown out the window when profit is involved, driving iconic wildlife such as African elephants toward extinction.
“Making money off the opportunity to kill these animals for bragging rights is something that most people find appalling.
“It’s an elitist hobby of the one per cent, and there is no place for it in today’s world.”
Audrey Delsink, HSI Africa wildlife director, said: “South Africa’s benchmark role in the captive breeding of lions for trophy hunting is a conservation and welfare disgrace.”
Nevada law makes it illegal to buy or sell parts of species including lions, elephants, rhinos, tigers, leopards, rays and hippos.
The Independent has asked SCI to comment.