Garchomp isn't able to learn Dragon dance, so breeding with him won't work. Haxorus Is the easiest one to breed with since he can learn it via level up. There are a few others here you can check out too.
In order to copy the nature, (only a 50% chance per egg) make sure the everstone is on the female pokemon, who should be Tyranitar in order to breed a Larvitar.
If you get lucky enough to get a breeding partner with a high IV in whatever stat you want, then give it a power item (brace, anklet, etc) and that IV will be passed on to the pokemon you breed.
Hope this helped a bit.