The sport gas pedal is still available through Lexus, just not by itself anymore. Lexus changed the design and no longer offers the pedal separate from the lever/arm assembly. The assembly is $410.00! Hardly worth it.
tqlla3k is right, the 1st gen. IS pedal is exactly the same and also comes as part of the assembly but it's only $70.00. You have to remove the pedal from the bar and re-attach it to the one in your 2nd gen. IS. It's a royal pain in the a** but it can be done.