Safari Press usually only has their latest releases for sale. Older books need to be purchased second hand from Ebay or other places.
They do have an affiliate, Worldwide Hunting Books. This is a good resource for antique and out of print books.
https://www.worldwidehuntingbooks.com/
Another place for good books is Sporting Classics. They have both regular print editions and limited editions for sale.
https://sportingclassics.com/
My personal favorite is Abe Books. Here, all the small bookshops of the world post their books for sale. Great resource, but you need to know what you're looking for.
https://www.abebooks.com/