They are randomly spawned at Marsh only.
Viewing post in Old Bug Report Thread
ok....... not sure why they aren't purchasable when so many other odd races are and i tried the marsh already quite a bit but i'll try again, maybe i just had bad luck. I did finally find one though i think they may be rarer than demon or lamia at least by what i encountered. well thanks in any case, now i know they can be found ;p