Use your Google-fu.
Hornady 82198 - they have allegedly 37 BOXES in stock right on my first hit:
300 Winchester Magnum by Hornady  - $33.90 : ESC, You decide.We provide
Buy several boxes if you shoot factory ammo and don't want this problem again. Oh, and from experience, CALL them to order, verifying they actually have it in stock. Going through the next few pages of a Google search shows no one else has it in stock so I wouldn't assume the web page linked above is up to date.
That's probably as good as you're going to get unless you move to a different ammo.
Alternately, if you know anyone who reloads you can work up a load using 180 Accubonds as they are probably as close as you can get.