A translation from the JR Central Website (Courtesy of Google Translate, so it is bad) should see the last run (Retirement Event) on the 16th March as Nozomi 329 from Tokyo to Shin Osaka.
News release can be found at: http://jr-central.co.jp/news/release/nws000924.htmlJR Central wrote:1. Retirement event
(1) The final draft of the 300 series cars
Sun March 16, 2012 final draft (Friday)
Last Armored Train extraordinary - "Nozomi No. 329" ("Thank you 300 series" Nozomi)
Tokyo operation interval (from 10:47) - Shin-Osaka (Arriving 13:23)
From Tokyo Station, departure time and 10:47 停車駅 · 10:54 from Shinagawa Station, from Shin-Yokohama Station 11:06, 12:32 from Nagoya Station
13:08 wearing Kyoto Station Shin-Osaka station wearing 13:23
- Other seats all cars driving by (date released: 16 February 1949 10:00, 2000)
Customers take the ※, presented a souvenir to ride. (Internal distribution between Shin-Yokohama to Kyoto).
This release does have more details of the retirement of the train including celebrations and runs the train will perform, however it is all in Japanese. If I see word of a JR West retirement I will let you know, but it says on Wiki (Unreliable but still a source) that they will be retired in Spring 2012 (So not long after the JR Central units, or maybe even at the same time). The JR West units are to be replaced by 700 Series units from JR Central, who in turn will have new N700 "Advanced" series units built for them. Last time I was in Japan I only caught sight of one 300 series unit, this was when I passed it at Odawara on my way to Tokyo to fly back to Australia. Even though I did hang around Shinkansen platforms I did not see any others roaming around, which does lead me to believe with the increased N700 deliveries the trains are only used on few services per day. The 300 is one of the last with character by way of sound on the Tokaido and Sanyo Shinkansen, the 500 being the other with awesome sound. The 700 series and N700 series are very quiet compared, however I did get one on my way back to Tokyo which was screaming out of stations so not all hope is lost! I have been lucky to get a video of a 300 series departure, for those who have not heard the sound of one before this is what I am talking about: http://youtu.be/CaXX7oSoTZ8