According to Springer’s Copyright Transfer Statement “Authors may self-archive the Author’s accepted manuscript of their articles on their own websites.” So I went ahead and created a new section here on my blog dedicated to the primary sources that I edited and translated over the years. For now you will only find the recently published letter from Husserl to Brentano there, but I plan on adding more material in the coming weeks. Moreover, once I figure out all the details, I’ll also add Open Access versions of my own articles.
Technically all of Brentano’s and Husserl’s writings are in the public domain according to european copyright law, but physical access to the sources is limited by geography. Brentano’s manuscripts and letters are in the Houghton Library at Harvard, though digital facsimiles are also available at the Brentano-Archives of the FDÖP in Graz. Husserl’s manuscripts and letter are kept at the Husserl-Archives Leuven, but digital facsimiles are available also at the Husserl-Archives in Cologne and Freiburg. Again, technically, the copyright on editions of previously unpublished manuscripts is only 25 years from the year of first publication, so you would think that all the Husserliana volumes published more than 25 years ago would be completely free. However, this does not take into account the added work of the editors: extensive critical notes, cross-references, modernization and correction of spelling, etc. and excellent historical-critical introductions. Nevertheless, the works published by Brentano, Husserl, and others during their lifetime are often freely available on-line (see e.g. the sources on Brentanist mathematics for examples). Additionally, Springer does make the front-matter and back-matter of the Husserliana (and Phaenomenologica) volumes freely available. This includes the editor’s introduction, the extensive critical note apparatus, various indexes, and sometimes original texts in appendix (for instance, the back-matter of Husserliana Materialien I, i.e. Husserl’s 1896 logic lecture, contains the entire substantial fragment of the 1895 logic lectures).
Some good places to search for public domain sources that I found very useful are e.g. Archive.org (if Google books has it, but doesn’t make it fully accessible, even though it should be in the public domain, chances are you can get it here), the Max Planck Institute for the History of Science, and the french national library (which has the Vierteljahrsschrift für Wissenschaftliche Philosophie).