Moomins and the Great Flood, which comes in the series of original books before Comet in Moominland is hard to get as well.
An absolutely brilliant set of books. There’s never been anything like them. Especially the last book where one of the fans of the previous books sort of wanders into Moomin Valley and learns to use the fantasy world as a launching pad into and not a refuge from the real world. And for all that they’re weird little Finnish trolls the Moomins in the books are a very realistic and heartwarming family. For example, Moomin Papa goes completely off his rocker during his mid-life crisis and Moomin Mama, while showing signs of the stress of being the sane one who has to keep things going, is a model of love and support.
The arc of the series, from super-happy pixie-land to growing up, follows the arc of the author’s life: from finding True Love to watching her lover die.