gm/regal antenna extension

I haven't ripped out the guts yet to install my stereo because the DR. http://www.installdr.com/InstallDocs/GM/Regal.html says I need a 3 foot antenna extension for the antenna adapter,which I'm having problems finding.

Anyone who has been "IN" there know if I really need it, or a work around ?

If this should be in old thread please move.
Thanks