There are a couple of "bare bones" laptop manufacturers that can give you OEM-type empty shells with a mainboard, screen and battery. The only options you have to customize are in the memory, storage, optical bay and operating system. Some might also allow for different processors through a socket (even though for modern systems this will allow you to choose your clock speed mostly).

I suggest you look for a distributor or importer of components who can supply these bare bones chassis laptops.

Update: A couple of manufacturers of these: http://www.clevo-computer.de/ and Mitac/Gelac from Taiwan.