These annuals, especially the early ones from the 50s, turn up on eBay UK (and on eBay USA at fantastically inflated prices!) though mostly in lower grades. The first annual is genuinely hard to get, especially in high grade. The 1997 annual was titled The Official Superman Annual and the 2007 one was Superman Returns based on the Brandon Routh film.
The Man of Steel movie also helped interest in these annuals and Superman vs Batman in 2016 will be useful.
See also Superman Storybook Annual 1968-1970 published by World Distributors.
Note: some PR issues may have no value. Selected issues in FN, VF or VF/NM may not exist in some titles.