From Nature:
No. Contrary to initial reports, the radioactive substance that last month killed Alexander Litvinenko, a former Russian spy who had been living in London, could probably be obtained by someone without contacts at nuclear reactors, the sites at which polonium-210 is manufactured. In the United States, tiny amounts can be bought from various supply companies — but one would need to buy thousands in order to amass a dangerous dose. Larger amounts of the substance are found in some commercial products, such as anti-static devices used by the plastics industry. These devices are strictly regulated and are usually only available for lease rather than purchase. Specifications available on manufacturers’ websites suggest that they contain enough polonium-210 to kill someone, says Paddy Regan, a physicist at the University of Surrey in Guildford, UK.
How much was used to kill Litvinenko?
No one knows for sure, but the time he took to die — around three weeks after being admitted to hospital — gives a rough clue.
More here.
