Over the past decade I've been collecting out-of-print and hard-to-find New Zealand crime novels. Even keen booklovers in New Zealand who like mystery fiction often think the history of the genre in our country is basically Dame Ngaio Marsh, one of the Queens of Crime of the Golden Age (wrote early 1930s-early 1980s) then Paul Thomas shaking up the local genre in the 1990s with Elmore Leonard-esque hardboiled tales, a few other one-off books here and there, then the recent surge post millennium.
But in fact I've discovered over the years that we had many other Kiwi mystery writers over the decades, some who wrote 10-15 books (even 30+ in one case) that were popular and well-reviewed at the time but have fallen out of print and been forgotten. So I keep my eyes out whenever I'm home and browsing secondhand bookshops, and nab any such books when I can. I probably have over 200 now from 1950s-1990s.
I also like collecting crime fiction from the places I travel, grabbing local stuff that may not be as widely distributed elsewhere.