There is a parallel cross-factions market on Nar Shaddaa, The Hutt Trade Network, with a totally different database.
It allows any faction to buy or sell there.
At the moment, it is not used a lot, and mainly for relatively low items but it's probably because most players are not aware of its existence or haven't understood yet what it is.
So it's certainly worth a look form time to time but it could maybe also be used to trade with your possible Empire characters. Not totally sure how: you would have either to be very fast or set insane prices for what you want to trade. (?)
It's located at The Promenade, on the lower level. See screenshots.