I never knew they made music stand lights, but I guess it makes perfect sense, since music is often played in dimly-lit music houses.
If I was faced with this problem, I would probably do a DIY solution involving off-the-shelf parts. For example, Nite-Ize has a few LED modules that contain the electronics and emitter(s) for very cheap, there's a Craftsman module that's also quite good, or you could try a MagLED module. Solder some wires to it, connect it to a switch and a battery carrier (or just a 9V batt for some setups), and you're good to go. If you wanted to get fancy, you could get some JB Stik Weld and create a custom mount, perhaps supergluing a magnet or velcro to it.
...Or you could just buy a ready-made music stand light. :shrug: