The Paizo threads have seen some wonderful homebrew content published that fits the Devaia campain setting well. I provide links to it here, so that you may all see and make use of it.

First off is the Armored Engineerbase class by Fniperknackle. It fits absolutely perfectly. Unlike other classes, this one should not get a defense bonus. It should keep it's armor bonus.

The Gun Mage by Detect Magic is very good for people who want to play the magus class. The standard magus is highly focused on melee, and in a firearms heavy setting like Devaia that can be an issue. The gun mage, however, is a very nice fit.

The Arcane Mechanicis similarly good.

The Gun Mage and Arcane Mechanic are both from a Pathfinder conversion of Iron Kingdoms, but they work very well in Devaia.

Here are some more homebrew works that fit:

Engineer base classby Anthony Kane

Artifice oracle mystery by Pluvia33

Ardwright base classby Paul O'Connell

Artificer base classby Nomadicc

Artificer base classby Witchfinder

Arisan base classby Witchfinder