My GS430 Y-pipe before the cat. converter has couple holes in it. Beside buying the factory one which cost around $400, who else make one aftermarket for that piece (prefer simple bolt on without buying the whole cat-back system)?

It is the piece #8

Thanks

 

jbrady is working on one...you should read his post. You can't just slap any aftermarket one on because of the low end torque you'd lose if its not done right.