There are many places to get samples. You can go "Crate Digging" which is when you look through vinyl to find samples. One of the more modern ways is to go through sites like Youtube, which features a sidebar to the right that contains videos that are similair to the one you're currently viewing. You can click through almost infinitely to find a good sample.

If you'd like to work smarter, not harder, you can look through forums where people will make threads with beats they'd like others to sample, or have sampled themselves. This allows you to find beats with great sections to sample.