How Can I get admission in Post-Doctorate?

You're going to have to see if there are websites listing postdocs in your field; that's what they do in my field, but it's not business. Postdoc money isn't always available, so when it is people post ads for them, but you can't expect any one school to be constantly accepting applications. And postdocs in the US are far more common in the sciences, math, and engineering than they are in things like business.