The hardest part is knowing what you need. Parts can be found by simply googleing them.

Any vendor that deals in old trucks of the era will have parts.

I got my entire master rebuild kit from Clegg for $700. Nothing special about it.

If you need help with performance or 'what goes where' then google is still your friend.

I'll price out as many vendors as I can to get the lowest price. And ALWAYS check shipping costs. The lowest price may be a huge rip off when you add in shipping fees. Generally anything over $150 order better be free.