There's an active mirror of asstr in www.asstr-mirror.org/

Be forewarned, it's not https.

I've found that both the file browser on the entry page and the search function once you've entered seem to work (there was one person within the file browser I found who didn't have any working files, but I wasn't familiar with their work so it's possible they didn't make anything)

Unfortunately, none of the pages on the front page appear to be linked properly