So by some miracle, David had the 230gr .375 plainsmaster bullets that I wanted. He doesn't normally carry them, but had some on hand.
Looks like Discreet Ballistics does try to carry the .264 (124gr) and .308 (167gr) plainsmaster bullets. He said he could maybe get some other calibers/types if there was a demand. Shipping from South Africa can be costly for small batches, I suppose.
I would say, if you are interested in Peregrine bullets, then let him know. Even if he doesn't have what you want, it may give him an idea on whether there is enough demand to stock different Peregrine bullets. Their main focus isn't on selling Peregrine bullets, so thats why they only carry the two projectiles.
Please note that Discreet Ballistics' main thing is subsonic hunting stuff. That kinda sounds fun. Its not long range hunting, but it would be a challenge. Quiet, too.
I will try to post a pic of what he is sending me.