With the exception of special sales, the team at Cloud Imperium Games have removed both 350R and M50 racing ships from their online store. However, this has not stopped the developer/publisher from releasing a big pile of in-engine rendered artwork on their website for both ships, which can be found HERE.
While the 350R and M50 racing ships are no longer able to be pledged for, they will be available using in-game credits when Star Citizen launches in 2015/2016.