The Internet Archive has PDF scans openly available for each of the first three volumes of Hermann Strack and Paul Billerbeck’s Kommentar zum Neuen Testament aus Talmud und Midrasch, 6 vols. (München: Beck, 1922–1961):1
In addition, there is also a combined PDF that includes vols. 1–3 and2
Each of the files is reasonably large (75.7–134 MB). So, they may take some time to load on slower connections or browsers.