To the best of our knowledge, uranium has the highest atomic number of naturally occurring elements (Z=92). Anything above that (93 - 118) was synthesised in a particle accelerator. There's no reason why we can't continue to do this with higher and higher atomic numbers but most of the nuclei are so unstable that they only exist for a fraction of a second before disintegrating, so they have no practical uses. There is a hypothesised "island of stability" where some semi-stable nuclei could exist with longer half-lives but again it's unlikely that anything will exist long enough to be useful.

So we MIGHT find some new elements out in space but they'd almost certainly be synthesised by an alien race and be extremely short-lived.