Heroes of Might & Magic III: Horn of the Abyss

where can I download the complete collection (there's no SoD separately, only the complete version)?

you can download a clean SoD version somewhere in this area, which you can then install HotA on. but by downloading these files, anyone is essentially violating copyright, after all. the game may be old, but Ubisoft hasn't released it as freeware yet.