Does anyone know where...

Most -- if not ALL -- of the time , the different states don't even recognise pre-1981 , 13 digit v.i.n.'s !!

I've tried to search for my '72 Dart and '73 Duster , but the Ca.'s DMV only provides for the 1981 & later v.i.n.'s .

Your experience is typical of most DMV's (and government organisations in general ) :
" Don't Think Outside of the 'Rules' ! "
I'd even recommend looking for images on Google ( et al. ) where a '67 & earlier v.i.n. is shown ( lower "A" pillar ) without these alleged rivets .