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The problem with finding it used to be that the various hypothesized locations were surveyed and nothing was found. IRAS covered quite a bit of the sky and didn’t find any telltale infrared. If the companion is in a polar orbit, it probably would be missed, an idea which came from the discoverer of Pluto, who continued to survey the skies for years after his discovery. Perhaps the construction of those big scopes in the Andes (the southern hemisphere having much less landmass and population, some of the sky had been neglected) and these orbital observatories will find something. Hey, if everything was known, there’d be no reason to build stuff like that.

The European Southern Observatory (ESO) was built at the Atacama Desert in Chile for these reasons: 1) They needed a modern observatory to cover the southern sky, 2) the location had some of the lowest interference from the refraction of the atmosphere due its high altitude and extremely low humidity and 3) the observatories could be reached from Europe in under a day's flight time. In fact, they're building even more telescopes at that location.

But now that new telescopes that can scan the entire sky from one location will come online within the next decade, and the launches of the Wide-Field Infrared Survey Explorer satellite, the ESA Herschel infrared satellite, and the James Webb Space Telescope should finally get the tools to prove or disprove if we have a brown dwarf companion to our Sun.