Calif FTB wants me to file 2006

neither Turbotax nor the IRS keeps returns that old.   I don't think the forms are available online or by phone so you'll have to request them by mail

https://webapp.ftb.ca.gov/contactus/home/formsbymail 

do your best.  I would also attach a statement that says "actual tax documents from 2006 are not available. i used my best effort to estimate the amounts reported"

are you sure it's actually from CA FTB, I mean almost 15 years is a long time for them to wait?

There is no Statute of Limitations with California FTB if you failed to file a 2006 return in the first place.

https://www.ftb.ca.gov/file/after-you-file/audit/index.html