Sorry, I meant the opposite. What would a good source be? Isn't Tesla the primary source of such data? Where else would you expect it to come from?
Overall, I doubt that there's a problem. If there were substantial numbers of significant accidents occurring on public roads that weren't being reported, I think someone would be catching reporting errors. There are a lot of very interested parties watching autonomous vehicles. (competitors, media, etc.)
The implication seems to be that Tesla are lying about accidents. It seems like that would easily get caught out. Accidents tend to be things that happen in public.