I need to find the ground effect piece that runs along the bottom the the door for an 85 IROC. Where would i get a new or used piece like this?

 

I think they sell them at the Piggly Wiggly

 

You can find them at various places including these:-

http://www.hawksthirdgenparts.com/
I have not personally used them, but they are a sponsor of ThirdGen.org and I have heard many good reports regarding them a friend.

www.thirdgenusa.com
This is IrocZDaves website. I've used him for vaious pieces and the service is exceptional.

Hope that helps you!