Former GC Holder

I was transferred using a L1-B in 1999 and obtained my GC in 2002. I moved back to Canada in 2003 for a number of reasons and now am interested in moving back to the US. When travelling through the border in 2006 I was asked to fill out paperwork for abandonment of status which I did without knowing any better.

I am wondering if anyone might know of some of my options at this point? Do I need to start over or are there alternatives that might allow me to get my GC back?

You need to start all over.

If its any consolation, your GC was already dead when you filed the paperwork -- you had in fact abandonned your GC -- you were simply confirming it.