I want to play an ice gnome (Barbegazi) in our new adventure path but I cannot find anything about where in Golarion they come from. I've already searched heaps of wikis without success. Where are they native to?
As your link shows, ice gnomes are a creature from a third party monster book (Tome of Horrors). Therefore that race isn't canonically native to Golarion. You can of course propose a likely location of your choice for your campaign.