http://www.mattsclassicbowties.com/
I've bought from these guys this year. Great prices and service.
Look for Goodmark sheetmetal.
As for original parts, the sources are limited, but look for junkyards in the Southwest part of the US. Less rust to fix, especially if you are paying someone by the hour to do your bodywork.
You are lucky that it's a '70 you are working on, the parts availability both new and used seem to be better than other years.
Good luck.