Flyfishing hooks usually can be found down to #18 or #20 in most outdoor stores which will work for most aquarium fish that are resistant to other types of removal (these will need to be de-barbed or have the barb crushed for the safety of the fish). Hooks at least as small as #30 are available online - side note: pre-snelled hooks are worth it for ease of use. To find really small fishing gear then search for “microfishing” or “Tenkara”. I personally recommend
tenkarabum.com for all microfishing gear (rod, hooks, line, floats, info, etc.) if your serious about catching fish in the 1” to 3” range.