One of the goals of Teletype.net is to archive as much teleprinter-related information as possible for preservation. To this end, I've established a special crawler that parses known teletype-related sites and backs them up redundantly. Even if the site only has a few pages directly related to teleprinters, I'll usually mirror the entire site. In the event that the site becomes permanently unavailable, I will upload the latest snapshot of it here.
Yes, the Internet Archive most likely has also archived much of these sites away, though it is known for missing pages. This way we ensure we archive everything we possibly can. It is impossible to save precious data too redundantly.
List of Mirrored Sites
Currently all sites are functional; if any disappear, we'll make the mirror available here