I’m not sure whether Shadow Wolf ever uploaded the extension (which is his modification of Simple Chat) to one of the usual places.
In this post here Menu based conversations - #15 by Shadow_Wolf, he links to a version on Pastebin: Activity Based Simple Chat for Inform7 - Pastebin.com
But as you remember, we found a bug in that version, which we fixed with the help of @Draconis here: Menu based Conversation system also accept a blank choice - Inform 7 - #7 by StJohnLimbo (there’s a file linked in that post).
I don’t know if it works with the latest version of Inform (v10.1.2).