Not just dogs. I’ve seen two cases reported of Electricians chewing on bits of wire: one of the reasons is that the lead content in the pvc made the plastic slightly sweet. I imagine that this is also a factor with the dust/paint poisoning of young children.
Regarding other sources: the lead from gasoline settled in the dust around roads with heavy traffic, as did the dust from the brake pads (which sometimes used to contain lead as well as often containing asbestos).