Yeah, they're third party. Mongoose Publishing, Encyclopaedia Arcane series. They also have an Encyclopaedia Divine series. Mongoose Publishing has some good books, but mostly, I use them for themes and such. Star Magic - Wisdom of the Magi, for example, I used to define the culture of a race I made that believed that their goddess and the secrets of magic lay within the stars. Some other gems are Nymphology - Blue Magic (snerk), Crossbreeding - Flesh and Blood and Blood Magic - Oaths and Sacrifices.

On the allomancy-gnome thing, it could still be a animistic/shamanistic society. It could simply be focused on the spirit and element of metal (wu jen anyone?). After all, if contact with metal gives them power, there has to be some sort of power to the metal, right?