There's really no way to know. Ma Mopar never kept any numbers on how many cars were painted a certain color.
My '72 was originally petty blue, now painted B5. It doesn't seem like there are a ton of B3 (petty blue) cars out there at shows etc, but a lot of people repaint using high impact colors. So, unless you look at all the fender tags it's hard to say. I do see more a-bodies that are still Petty blue, but I think that has a lot to do with the E-bodies being repainted.