actually, you can rebarrel a 99 to 243, 308, 284, or 358. the 99 came in all of those. you will need to change some mag parts too, but they are available.
the 300 savage is still popular enough that I would leave it alone. you can get ammo for it pretty easily. it's a good round, anyways. I am reworking one, and leaving the caliber alone, at 300 savage.
caribou are not known for being tough, I wouldn't hesitate to use a 300 on one. just shoot good 150-gr bullets.
FWIW the 7.62x51 NATO round was developed from the 300 savage, and the 308 win from that.
of course, if you want to go all out, get one made for 308 and rebarrel it to 416 McPherson (.416/284). that thing packs a wallop.