Hi,
I know this is a bit late, but I've only just seen your post. I don't know how many Bridgestones were sold in the US, but I have seen a 1989 article from a Japanese magazine (written in Japanese) which gives some figures for total production and individual model production. As far as I can tell, this gives a total of 599,828 BS motorcycles produced from the original 1958 "Champion" through to the end of production in 1971.
What this doesn't include is the 30cc, 40cc and 50cc "Bambi" Bicycle power packs that Bridgestone built during the 1950s, before they got into building motorcycles. It is conceivable taht they would have built a lot of these power packs so they might bring the total of "motor driven units" up to the million mark.
One surprising thing I can tell from the figures is that the rarest model seems to be the BS200 - they only made 7,800 of those. Even the BS350 was built in greater numbers than that at 10,500.
I hope that helps!
Graham Weeks