The primary issue with many of the advanced forms of hydrogen and helium that humans need for fusion is that those elements do not exist in great profusion on Earth. This might seem strange, for hydrogen is generally considered to be widely available, but for fusion humans would much prefer to have isotopes of these elements. These isotopes are primarily deuterium and tritium, along with helium 3, which are much more effective in an engine, for a variety of reasons that primarily have to do with how the energy from the fusion reaction is allocated.
As is probably apparent by this time, while these elements do not exist in great profusion on Earth, they are available in mineable quantities in the solar system. In this case, the primary location is on Uranus, where they could be acquired via devices attached to dirigibles.
Of course, Uranus is a bit far away to place a mining platform there just at the moment, but it is interesting to note that whenever humans discover a technology that needs more of a resource than we currently have available, that it inevitiably exists somewhere inside the solar system in profusion.