As
@TinoPup has said, the entire population is owned by a private entity — the International Animal Exchange (IAE). The only on display animals are the 0.2 at their facility (African Safari Wildlife Park in Sandusky, Ohio) and the 1.4 at Zoo Miami. The rest of the population, ~ 40 individuals are all housed privately, split between two facilities.
It is nearly impossible to import bovids into the United States due to all of the restrictions in place to protect the cattle industry. It is prohibitively expensive and the paperwork and legal hoops to jump through are mountains high. In the case of the giant eland, the only other captive individuals are those in the UAE, which are descendants of the American stock. There are some more intensively managed wild populations of eastern giant eland in their native range, but importing wild animals from politically unstable countries isn’t going to happen.