This has nothing to do with WordPress, so I don’t get why you’re expecting to find a WordPress plugin? What am I missing?
why not…?
There are regular RSS plugins, maybe there is one that features ftp sourced RSS. If not, what would be the best way to go about it?
why not…?
There are two different things when it comes to RSS: syndication vs publishing. You seem to be confusing the two and where a WordPress plugin comes into play.
A WordPress plugin can fetch or syndicate an RSS feed from an external website that already supports RSS feed… and add the content it fetches to the WordPress site. This is RSS syndication. But this is not what you’re asking for.
You want to create or publish an RSS Feed for an external site (FTP or web, doesn’t matter) that doesn’t already publish an RSS feed. The work to add the FSS feed to the FTP site has to be done on the FTP site itself, not on an external WordPress site.
Again, FTP vs web is not the issue here. It’s RSS publishing vs RSS syndication. The source site, ie, the FTP site, needs to publish the RSS feed.