Kind of a niche request, I think, but some of my favorite books that fit the description are:
The Dragon Behind the Glass by Emily Voigt (about the arowana trade and this guy obsessed with finding a rare arowana)
The Orchid Thief by Susan Orlean (about this guy obsessed with orchids)
The Feather Thief by Kirk Wallace Johnson (about this guy obsessed with fly fishing)
by Large_Advantage5829