We have had difficulty getting our hands on these issues, though (or scans of them).
It's interesting that AMC just launched a series featuring Sam Spade this year, the year before the character goes into the public domain…
Black Mask is pretty rare. Brooks Hefner at James Madison University oversaw the acquisition/accession (I think) of their Black Mask collection, of which they have quite a bit in comparison to other places, but it's still incomplete. The Ransom Center in Austin specializes in rare and collectible items, but only has one or two issues. The Library of Congress may well have a complete collection, but what they do have isn't digitized because the pages are brittle and are literally falling apart (even moreso than other/older printed material).