Most of the time the rebels got ships from factions that were leaving the Empire (Mon Cals and Bothens as example). If they did "steal" something, typically they only stole the design or a prototype (like the X-wing).I kinda lol'd at that zero-g storm trooper.
The problem is though, how do you translate such things into gameplay? How do you make it so that when the empire starts research on a fighter, the rebels can come in and steal it? That's why I suggested the stealing ship, it may not be as realistic, but realism sometimes can not be fullfilled.
Also, an era suggestion could be late in the Legacy era with the new galactic empire and the Galactic Alliance. Would be three factions, Xel's insurgency, the Galactic Alliance, and Kraytes Empire. Every other era has been done atleast several times, but the Legacy era has only ever been touched on mildly in it's premier comics.