Thanks for posting this. My parents have original bicentennial copies of Harper’s Weekly, hidden somewhere. I use to look them over when I was kid in late 60s, early 70s. They were going to sell in late 80s or early 90s but not worth much. Not sure what other dates they may have other then 1876 or what shape the papers are in now.
Harper’s Monthly Magazine is still published. They have their entire archive available online (for price of subscription). Harper’s Weekly stopped publishing long ago. That archive is available at archive.com, except for the first year of publication, 1857. The problem with them is the pdf copies are such small scale they are very difficult to read.