Hello, and welcome to the forum. I have been keen to build a 40 for about 10 years, but it is getting very hard in Australia to build a car that is an accurate replica as the government keeps changing the rules on us.
For example, we cannot register a new car using the small block Ford engine because itis deemed not to meet the required emmission standards. My state government had now decided that to register a new car from January 2010, it must be fitted with 9 or 10 airbags, ABS and stabilty control. Whats worse, it seems to be having some success in trying to convince the other states in Australia to do the same.
I mention these issues as a reminder that you want to know what is allowed in your country before you become too committed to a build.
I am not sure from your question whether you are trying to locate specific parts for a project that you have underway, or some general guidance about parts and kits in general.
The forum has a section
GT40 Replica Manufacturers' Corner which supports builders of five different kit suppliers, and the banner ads at the top of the screen include these and other suppliers.
Some people on the forum are developing cars on their own, but starting with a kit is more common.
In relation to steering/suspension components, these really have to selected as part of the overall design concept. Some kits use Corvette components, some British Ford components, and others use custom machined or custom fabricated components.
Common transmissions are sourced from Porsche, and Audi cars with some modification, while some people stick with ZF transaxle used in many of the original cars.
The forum also includes discussion areas for engines, transmissions, suspension, chassis and body etc, which contain a lot of information about these elements of the car.
Hope this helps you in some way.
Mal