Most of the transuranium elements occur "naturally," (a definition that only makes sense if we exclude humans from nature, which is a nonsensical idea) but their half-lives are so short that beyond plutonium they're very rarely (or never) observed outside of nuclear reactors or accelerators.
All that is necessary for an element to go into the chart is that it exist long enough to be reliably observed. For UUO, (118) the half life is believed to be <1 millisecond.
So, then the elements are created by experiment with the belief that they would exist anyway. Or maybe they exist in great numbers if right the conditions exist, for example: they exist in a super nova, etc.? Or maybe during the formation of a black hole?