Approved Medicare Assistant surgeon codes

Maybe it's me.....I cannot find approved assistant surgeon codes on the CMS website. More often than I care to say, I will bill an assistant surgeon code and get denied saying the procedure does not call for an assist.
Does anybody know where I might get a list of codes?
Thank you.

Assistant at surgery

You can download the Medicare Fee Schedule, or look up a single code. This is the source documentation for the data. It is a large file.

Many vendors sell this information, as well.

You can download the Physician Fee Schedule at:

http://www.cms.hhs.gov/PhysicianFeeSched/PFSRVF/list.asp?listpage=3

You'll download a large file, zipped. After it unzips, there will be 16 files. Open the one named PPRRVU09.xls (Why couldn't they have named it something in english?) That's the Medicare Fee Schedule with everything in it. There are GPCI files, and location files and anesthesia files, and some OPPS files. The RVU file is provided as a pdf, excel or txt file.