Go to Federal ammunitions site, click on rifle at the top, on the left side when you scroll down you can refine by "caliber," do this, select 375 H&H, they have several loads available, even some of the less expensive powershok though nothing is inexpensive these days.
I think they only had the federal fusion available in the 300 win mag.
Must say, 458 lott ammo is certainly still available all over, though at times over 2 times what it was selling for before this mess, $12 or so a trigger pull for a lot of the stuff. Some deals still to be had out there.
I don't envy you 375 guys, they really seem to be out of stock a lot of places, not even price gouging seems to be stopping you guys.
Anyways, go to Federal's site and get your 375 H&H ammo, and jesus, hurry, doesn't seem like time is on your side.