At least for American people.
If you already have Sonic & All-Stars Racing Transformed for PS3, but for whatever reason you don’t have your bonus edition extra DLC, now you’re lucky.
Spanish site Sonic Paradise reports that the DLC is already available to buy in PS3’s PS Store, at least in the American one, as it is absent from the European store for now. The DLC, included for free in the bonus/limited/special edition of the game, contains an extra track, Outrun Bay, and a new character, Metal Sonic. If you don’t already have those two, you can now buy it for 1’99$.
It’s only available in the USA PS Store, but it’s reasonable to think it will be made available for Europe and, probable, other platforms too, very soon.