I guarantee you, if you made the effort you could get hold of some. Just go down to a pub at a weekend and follow your nose, it really ain't hard. If you had the intention to try some then it would be really easy. And if you think prohibition actually makes it harder to get hold of drugs then you really are clueless,.
And yes there is a lack of education on drugs. For a start it is not even on the national curriculum, for another thing most of the education consisits of the "Drugs are bad mmmmkay" and the "just say no" sort. And finally those that would be getting into drugs are more likely to be skiving off school the very time these lessons would be taking place. if users are informed of the risks at the moment of purchase it works two ways:
1)It targets the people who need the education directly, as they are the ones having a smoke
2)It is more likely to sink in if it the information is given to them by a medical professional (eg a pharmacist)
And finally when it comes to cigarettes, the actual cost of manufacturing cigarettes is pennies, and the tax on them is exceedingly high. The high tax has led to a black market. The same would be true of cannabis if legalised at taxed. The government would have to make sure that they balanced the taxation demand with the need to stop the blackmarket. Cannabis is expensive at the moment due to the risk dealers encounter with regards to the law. I have no reason to doubt that legal cannabis would be far cheaper than illicit at the moment. There is also the point that yes there are criminals selling cigarettes but the vast vast vast majority of tobacco is sold over the counter, legally and brings in billions in revenue every year.