As someone else said before, there are too many to count, but it would be an interesting list.
One important OEM missing from your list is Mastech - there's also UEI (121GW is from them), Uni-T, Bside (I think) that has also rebrands such as Aneng, Richmeters, etc.
As for brands, Minipa has meters from Brymen, Uni-T and Mastech and maybe CEM. Another brand is Icel, which has CEM and maybe Mastech. Anprobe has both original and rebrands.
Digging through such list is a very involving work, but it may be quite interesting.