Reb Moshe has a trshuva in the sefer that it’s a treifah.
Can you please cite the source? It would be interesting to see, since Rav Belsky was mattir based on the animals not being treifah.
Therefore there is nothing to ask Reb Dovid Or Reb Reuvain.
This is a mistake. Even if the milk from DA cows us treifah, the containers of milk you buy in the stores could be muttar because of bittul. That is the psak of R’ Chatzkel Roth, and I assume the reason R’ Dovid Feinstein is in fact mattir.
The gedolei poskim in Eretz Yisroel were in fact machmir, so there is certainly reason to buy only CY even for one who used to be meikil, but it is false to claim that those who do buy CS don’t have on whom to rely.