Sneak preview: http://loyce.club/archive/oldposts/
How to use:

• Find the msgID you need. Let's use 28228
• Remove the last 5 digits from the msgID to get the directory name (if there are less than 5 digits, use 0): 0
• Replace the last 2 digits of the msgID by xx, and add .html (if there are less than 5 digits, use 0xx): 282xx.html
• Add "#msg" and the msgID: #msg28228
• Put everything together and go to http://loyce.club/archive/oldposts/0/282xx.html#msg28228

Limitations

• Currently, the first 2.1 million posts are available.
• I'll scrape the first 5.21 million topics and all posts in there.
• That means I'll archive 53.36 million posts, this partially overlaps with my scraper for new posts.
• This is a one-time thing, I won't update it with newer posts (I scrape unedited versions for those).
• The time "scraped on" is Amsterdam time.

If no username is mentioned, it's either "Anonymous" or "random". I forgot those exist when I started scraping, and it's not important enough to start over.

I found a bug (which I'm posting here as a reminder to myself): Posts on the עברי (Hebrew) board don't show up. Example: this post is missing, while it exists.
I'll see if I can add them later. I think it has something to do with the right-to-left writing, even selecting text on that board doesn't work as expected.
Update: عربية (Arabic) has the same problem.