more info that you probably care to know here.
in general from any of these places in china, i don抰 order if the item is not in stock. sometimes there is no telling when it may come in. even when in stock, expect a few weeks, maybe even over a month to get it.
can buy complete and replacement parts here (btw if you are new the hobby, and in the us, you probably want mode 2 if you see that listed somewhere and they have different modes): http://www.banggood.com/buy/hubsan-x4.html
i recommend only getting the new replacement prop, and pulling off the stock ones if you have the old x4 (no led抯 by all 4 motors): http://www.banggood.com/hubsan-h107-x4-rc-quadcopter-spare-parts-propeller-blade-set-p-72513.html these are a little longer on the motor shaft, and protect the motor from being destroyed if you land hard upside down.
old version of the x4: http://www.banggood.com/wholesale-h107-hubsan-x4-2_4ghz-4ch-rc-remote-control-quadcopter-p-59211.html
new version (stronger body, added lights, new props come on it) http://www.banggood.com/upgrade-hubsan-x4-h107-2_4g-4ch-remote-control-rc-quadcopter-p-71838.html
really cool first person view (fpv) one http://www.banggood.com/wholesale-hubsan-h107d-fpv-x4-rc-quadcopter-rtf-with-5_8g-fpv-6ch-transmitter-p-68571.html
alternate place for batteries:
no matter where you get batteries, make sure the polarity is correct!!! one brand has the same connector, but the red and black wires are reversed. this is easy to swap out, just push in a little keeper pin in the wire end, pull out the wires, and swap them.
since it takes so long to get things, i recommend getting replacements before you need them (waiting sucks). you will need props, get them. you will crash, depending on your experience, how often and how hard will vary. these are pretty durable, but not indestructible. the next 2 things i抎 recommend are a spare body and spare motors, both require soldering to replace though. the body can eventually break with constant impacts, or even on a really bad, or just right one. most glues don抰 stick very well, but some people have made temporary fixes. the motors are just tiny and cheap, qc can be hit or miss and they will eventually wear out (this time will vary a lot).
other quads that are pretty much the same, but the programming on the boards will be a tad different and they may fly a bit different.
estes dart quadcopter