The 1958-P Franklin Half Dollar has one of the lowest mintages in the series. It's mintage was 4,042,000 but if compared to other coins in the series like the 1963-D which had a mintage of over 67,000,000 the 1958-P's mintage is relatively small.
Most 1958-P Franklin Half's came in nice quality. Only in MS65 grades and higher does it appear to be scarce. In MS66 condition it is scarce but there are still hundreds of examples that exist in this condition. In MS67 condition they are very scarce with less than a few dozen known.