1958 is difficult to get in top grade, but why? According to the mintage figures, which are supposedly accurate for that era, there were more than 120 million minted. The young head Victoria series are also difficult to obtain in decent grades, ESC only lists 4 of the entire series as more common than scarce. 1860-70 (excepting 1864 & 1866) are probably the most difficult apart from the very rare years 1848, 1854 and 1879+DN. I've found 1960 in top grade hard to get.