I don't think there's anything stopping us from making trace amounts of elements heavier than iron. The superheavy elements have only been synthesised in the laboratory. https://en.wikipedia.org/wiki/Superheavy_element

Way easier to just electrolyze olivine, of which we have plenty. Downside is that you actually get more silicon and magnesium out of it, and those are higher strength each than the iron you get from each chunk of rock. I.e., if you wanted to use them to make a bridge, it'd be mostly of something like silicon fiber reinforced magnesium instead of steel. Unless refining them to sufficient purity turns out to be too difficult to be worth it.