I've gotten parts through LMC truck and have been very happy with their quality.
http://www.lmctruck.com/

I've also heard classic parts of America is good http://www.classicparts.com/download-cat.html
And so is Chevys of the 40's, they have things I never thought I'd find.
http://www.chevsofthe40s.com/

And I also found this place, but can't vouch for quality
http://www.brotherstrucks.com/

I've put together a parts list for my rig and prices very, one place is cheaper on somethings but not on others. Good luck!

1947farmer

1947 2-Ton Chevy
Story in the Stovebolt Gallery
More pix in Photobucket
1977 3/4-ton
1985 2.5-ton
2- 1947 Allis WC
1- 1949 Allis allcrop
1- 1955 Allis WD-45
1- 1976 Allis 7040

"If it ain't broke you ain't trying"