Buying or acquiring old animation for new animated TV Show?

I hope I´m posting this right. I wanted to ask if anybody knows or explain to me how I can use old animation/copyright free animation to produce a new animated show. If you still confused or I just didn't explain it good enough you can look at shows like Sealab 2021, Harvey Birdman or Space Ghost Coast to Coast. These shows are made from old reused Hanna Barbera Cartoons. What I don`t want is just redubbing the show, the goal is to have a wide range of animation to reuse and compose to a new show. I hope my question is understandable, thank you for you help :)