It was in a book on linguistics. The author was discussing how languages evolve and admittedly used flither as an example of a word whose usage had disappeared.
I don’t recall the specific book but it was probably something by John McWhorter or Stephen Pinker - I’ve read a lot of their stuff.
A flither appears to be a limpet.
Could it have been a misprint of “thither”? The fl combination is quite similar to a th combination.
I also fly a lot, both domestic (US) and International. The bags are generally there. When they aren’t there, IME, it seems to be more a question of used or taken then not yet re-stocked.
I may start collecting them. I’ll have to see if they’re amusing enough for the office. 
I have definitely seen them used. The fastest I’ve ever seen a flight attendant go from “what is it now - stop ringing that buzzer” to “oh yes I can help with that” was after someone started using one and several of us rang. It was bumpy enough that the person in question couldn’t get up and she really needed a hand (and more bags, poor thing).
Susan never vomits at home.