So per
chat.stackexchange.com/transcript/message/53625706#53625706 , I'm now looking on used book sales websites for Jules Verne,
A rejtelmes sziget (orig. "L'île mystérieuse") in Majtényi's translation, published after 1990, and a full version (not abridged). But the data about books in used book stores is often so lacking that it often doesn't list the number of pages, publication date, publisher, and almost never lists ISBN or translator name, so this is not easy.