Buy from iherb, pay for the cheapest shipping with tracking. The timeline: between 5 - 12 days to arrival.

Jarrows formula is a good brand that comes to mind quickly. If you want a better deal gotta look for yourself. 

Note: Melatonin is only for short term uses only, e.g. for quickly getting back on your regular sleep schedule after a 24 hr flight or multiple all-nighters at work.

Beyond that, your friend should be looking at lifestyle changes.