Reggie Foster did have a textbook come out before his death (unlike Ørberg's, which you mention, it is written in English rather than Latin), Ossa Latinitatis Sola.
He also had a sequel (about reading Cicero) in press which is due out in January. It's called Ossium Carnes Multae. Daniel McCarthy, the editor, has been collecting materials by Foster with the aim of bringing out a five-part series:
https://thelatinlanguage.org/ossa/
He also had a sequel (about reading Cicero) in press which is due out in January. It's called Ossium Carnes Multae. Daniel McCarthy, the editor, has been collecting materials by Foster with the aim of bringing out a five-part series:
https://thelatinlanguage.org/latinitatis-corpus/
I'm not sure whether volumes III through V are ever going to appear. :-(