Look in your Windows Defender or antivirus history.
Since v1.4.3580 is an older sub-version of the 1.4 "Biotech" era, most mods labeled for should work. However, if you are looking for a specific "piece" of content: Steam Workshop: You can filter by version 1.4. RimWorld.v1.4.3580.zip
It looks like you are referencing a specific archived version of (v1.4.3580). If you are looking for a "piece" in the context of a missing file, a mod, or a specific fix for that version, I can point you in the right direction depending on what you need. Look in your Windows Defender or antivirus history