Welcome to the board!
Ill be "that guy" that reminds the newbie the benefit of the "Search" feature.
if you search for thinks like "parts supplier" you will get a lot of threads on the issue, but since you asked, I frequently use:
www.classicparts.com
www.lmctrucks.com
www.classicindustries.com
I rareley use brotherstrucks.com because they have 30% inflated prices, then run 20% OFF! sales, where there parts are still more expensive than ClassicParts.com.
I have probably spent $4,000 at classicparts.com, they are my first source as they are out of state for me so no sales tax, and they have the best prices.
There are also some forum members that are parts suppliers, and they throw out deals to members.
Good luck with convincing the parents, and post some photos of this beast!