You're not the first person to search for classic car parts, and you can learn from those who have been down this long and winding road before you. In addition to swap meets and clubs, a good place to find these people is in online forums. The more specific the forum, the better (if you're looking for parts for a 1929 Model A, there's no point in joining the conversation about '68 Mustangs). Start your search with your make and model and the word "forum." Within a forum, you might even search for threads specific to the type of restoration you're doing, or you might find people talking about the specific part you need.
Remember, no one likes a poser. Read first. Be helpful when you can. And be specific, direct and humble when asking where users found the parts you need.