You are correct about Weatherby not making ammo for those cartridges. So I did a little digging. On the Weatherby site, under FAQ's, this is one question listed and the answer:
Does Weatherby® recommend specific ammunition for each caliber to get the best accuracy?
Following are some of the initial loads used in Weatherby’s shop when testing for accuracy:
300 Win Mag : Federal Power-Shok 180 grain Speer Hot-Cor SP (300WBS)
Federal Vital-Shok 180 grain Barnes Triple-Shock (P300WP)
7mm Rem Mag :
Federal Power-Shok 175 grain Soft Point
Federal Vital-Shok 160 grain Barnes Triple-Shock (P7RN)