wow, you got me. The fact that I can't personally purchase and own one of these humans means they're not slaves. As you know, the definition of slavery definitely includes something about slaves being bought and sold in a public marketplace.

> tell me where you can buy one to own as property

Just buy a judge or two.

Judges Plead Guilty in Scheme to Jail Youths for Profit: https://www.nytimes.com/2009/02/13/us/13judge.html

> tell me where you can buy one to own as property

The American prison slave population's value is packaged in municipal bonds.

So to answer your question, buy a lot of bonds and send labor contracts to the related prisons, a middleman called the US government will take care of the rest.