Yes, the place really does exist. There are several places of that name, but here's what Compton's Encyclopedia has to say about the one from the Illuminatus books:
Bioko Island (also called Fernando Po, formerly Macias Nguema Biyogo), Equatorial Guinea, island off west coast of Africa, in Gulf of Guinea; area 779 square miles (2,018 square km); population 63,000.
Bioko Island, known as Fernando Po until 1973, was administered by the British from 1827 to 1858. Through the early and mid-20th century, the site was called Spanish Guinea. By the 1970s Spain had relinquished most of its African possessions. Spanish Morocco, now part of Morocco, became independent in 1956. The provinces of Fernando Po and Rio Muni achieved independence as Equatorial Guinea in 1968. Independence was declared in 1968 and was followed by a reign of terror and economic troubles brought on by the dictatorial president, Francisco Macias Nguema. He was overthrown by a coup in 1979 and was later executed. Equatorial Guinea has since been governed by a Supreme Military Council and is attempting to develop democratic social and political norms and its economy. A new constitution was approved in 1982, and on Aug. 28, 1983, a 41-member National Assembly was elected. Population (1984 estimate), 325,000.
EQUATORIAL GUINEA. A republic on the west coast of Africa, Equatorial Guinea includes an area on the mainland called Rio Muni (or Mbini) and five islands: Bioko, Corisco, Great Elobey, Little Elobey, and Annobon.
The capital, Malabo, is on Bioko. Bioko Island is made up of volcanic cones, crater lakes, and rich lava soils. There is an extinct volcano in the north that is 9,868 feet (3,008 meters) high. Bioko Island has mangrove swamps along the coast and no big game. Other crops are bananas, grown on Bioko, Petroleum was discovered off the north coast of Bioko in 1981.
About four fifths of the population of Equatorial Guinea are Roman Catholic, but the Bubi people on Bioko Island retain their traditional forms of worship.