I'm not aware of an MB similar artist database. I'm guessing you used music map[0], it's the only free database I know of for similar artists that doesn't require scraping.
Ah, I think you're right that it wasn't MB because I remember having to match artists by name rather than mbid. Music map doesn't sound familiar but my boss negotiated the access, I think I was just ingesting the data from a csv dump so it could have been anywhere.
Around that time freebase was still a thing, and dbpedia/wikipedia could also be used to sample relationships.