It is best to check the latest version of the Peaceful Pill ebook and forum1 for current information before attempting to purchase from any source (although see the notes to Minimum lethal doses for information on lethal doses). Users on the forum often discuss most reliable sources to purchase this drug, and it is changing all the time. It is also worth noting that importing Nembutal into most countries is illegal, although Nitschke only cites one report of a person being prosecuted.
The information contained in the Peaceful Pill Handbook about Nembutal is regularly updated, and does include pictures of packaging. Anyone considering purchasing and using this drug would gain much information by purchasing the latest version of the ebook, as this is the most comprehensive source of up to date information about obtaining and using Nembutal.
Exit International (www.exitinternational.net), founded by Dr Nitschke, also offer a Nembutal testing kit, to check if the drug is (a) a barbiturate and (b) of sufficient strength to provide a peaceful death at the time of one's choosing. Given some people obtain Nembutal from uncertain sources, or store it for some time before use (it has a limited shelf life, although has been known to be stored for 15 years and still be fine), the kits were designed to reassure people that their Nembutal is still effective.
Derek Humphy's book Final Exit3 is also worthy of consideration for further information on drugs as a method of suicide. It is available as a book or ebook and periodically updated, although not as often as the Peaceful Pill Handbook.