A Kansas man admits he tried to buy two tiger pelts in violation of federal law. He didn’t know the seller was actually an undercover agent from the U.S. Fish and Wildlife Service.           Federal prosecutors say 38-year-old Ret Thach of Wichita pleaded guilty Tuesday to violating the Lacey Act, which prohibits interstate sale or purchase of animals covered by the Endangered Species Act.       In his plea, Thach admitted …