I looked at where to find Carnivine on this site, and it said it is a "daily Pokemon". What day? Is it even a certain day?
Question in simple form: How do you catch Carnivine on Pokemon Pearl?
You can catch Carnivine at the Great Marsh just by walking in the grass. The only problem you may have is getting one to appear, which is a 5/32 chance.
Source: Experience, Bulbapedia
Hope I Helped.