Thanks for the links. I had already tried the High Sierra one. And yet, the App Store (not "Apple Store") still seems reluctant to make these links available to me. Instead, it shows me an error and sends me to the welcome page, where a search doesn't show any options other than Mohave. Prob a bug with my apple id, because I've logged in and out several times (even tho apple id not required?). I'll give Apple Support a try. Thanks again.
Update: Apple support says that once my MacBook was updated to Mohave, the App Store will no longer allow a previous OS download to that particular machine. I'll just wait for the next UniBeast and stay grateful to MacMan and this board's other amazing contributors!