You can buy melatonin in a variety of doses over the counter. Its normally near the vitamins and supplements part of the store.

OTC melatonin has fairly unpredictable quality though. The amount of melatonin in the entire bottle might be correct, but the amount in each pill may vary wildly. You can get prescription melatonin that's actually controlled so each pill has the same amount in it.

Or you can get it in pure powder form and make your own dose (like http://www.powdercity.com/products/melatonin-powder )

Note higher dosing is NOT better...most OTC melatonin supplements give too much. 0.5 to 1.0 mg should be used 1-3 hours before bedtime.

1-3 hours? Do you have a source for that advice? Everything I've read, and my personal experience with it, suggests taking it (as you say, .5 to 1mg) 30 minutes before you want to fall asleep.

Personally I take it 45 minutes before expected bedtime (irregularly, only if I feel I need it).

I use a liquid form of melatonin. A dropper is included in the one I use. I found I could measure my dose way more accurately than breaking tiny 3mg pills haphazardly.