I think I would just cut a micro-usb cable in half rather than spend time searching for one. Even if you find a source I doubt if you'd save any money by the time you'd paid the postage and packing.
Yes, you can power the Pi via the 0v and 5v pins in the GPIO connector - with 5v, obviously - but don't get it the wrong way round or confuse the +5v and +3.3v pins - there is no protection!
Since you ask the question I'm guessing you may be new to all this. I would steer clear of direct connection to the GPIO connector, and home-made cables too for that matter, unless you are sure of what you're doing.