Gabor,
These are actually
Vietnamese coins not
Chinese. At least all the ones I can make out are.
I can see lots of Canh Hung Thong Bao (1740-1776) of Emperor Le Hien Tong and a few variants from the same time such as the Canh Hung Cu Bao.
They look genuine and are not particularly
rare or known to be widely faked. The CHTB are shown in over 80 varieties in
Barker's book with another 10 varieties of CHCB.
SC