Most of the time the aftermarket company buys them themselves. The only common exception is when a company develops an accessory that will be offered as a dealer fit or production line part. However, that is not an aftermarket part.

Cheers

Greg Locock

Like Greg mentioned, the vast majority of aftermarket vendors purchase their own vehicles. In many cases they have customers supply donor vehicles. The aftermarket company gets a vehicle to test, and the owner usually gets free (or greatly discounted) parts and service in return.  This is often the way to go for a small outfit with limited funds.

The only aftermarket companies that I am aware of that receive free (or severely discounted) vehicles are large integrators such as tow-truck, limousine, and fleet vehicle modifiers. In those limited cases, it makes sense for the bean counters to hand over the keys.

Good Luck
Bryan Carter

Here's how one big aftermarket outfit gets vehicles:

http://www.edelbrock.com/automotive/vehicles_needed.htm...

Ss usual Greg has it right.

The other thing that would help is a SEMA membership.

www.sema.org