You have to buy the gun first and then proceed with the transfer. Most shops ask for a certain amount of money up front before they look due to the fact that a lot of people want to buy one but back out or don't have the money. If you are serious check out
www.subguns.com and go the the NFA Add Board. You can also check some of the online gun brokers. You can find machine guns from anywhere around $1000 to $100,000 range. If you know what king of machine gun you are looking for and what price you have in mind to pay for one post back and I will see if I can steer you in the right direction.