re: 6.5-300 Weatherby Mag ammo?

As others have mentioned, if you get any ammo, be sure to retrieve and save all the brass, it’s worth about $2.00 a round for empty hulls.
Wildcat calibers are often harder to get than standard calibers but even more so during worldwide shortages like currently being experienced. If you aren’t real interested in getting into reloading, you might consider asking friends, co-workers, hunting club buddies if any of them reload and if so, would they be interested in loading for you for a reasonable charge.
Primers of any kind are almost impossible to get right now but someone already loading for a large rifle caliber may be willing to load you a box or two using their primers.