You can't get one off ebay that works off 12v that can push 2A out one socket (never mind 4 or 7) easily at all... even those with 2A and multiple sockets tend to split the charge by the number of devices, so something that is @a for one socket is !a x2 or 500mA x4 when all are in use.
DIY is probably the best bet by hacking up cigarette lighter units...

