are you talking about ship renders or the 'characters'?
Characters I find on google image search :P
Ships you can render easily in open singleplayer. Just turn your 'space background detail' in the options down to zero, and it replaces the background with solid black. Take a screenshot, then use photoshop or another image editing program to make the black portion transparent, leaving the ship in the image.
Speaking of which, I've updated my signature to include my two ships: