Yes melatonin is one of those "tricky" things to get a hold of. For some reason it is freely available in America, but in other countries it can be harder to get a hold of. I heard it had something to do with a bad batch causing some deaths in Japan, but that had more to do with the manufacturer than the actual product itself. It seems to be perfectly okay to push drugs on to people, but when it comes to something more “natural†they have a hissy fit.
In Australia you can get it on prescription only, so it is freely available, but you need to get it from your doctor. I use it as a compliment to HRT and while I'm reducing my dose of sleeping tablets. I take 2-4 mg for a couple of nights each time I do a reduction in the dose of the sleeping tablet I use to help me get used to the new dose. Hopefully within the next few weeks I'll be able to stop using it, and the sleeping tablets, all together.