It might help to know how this 'to your door' process actually works.

Assume you have a NFA manufacturer located in Oklahoma. Under the NFA they have to Form 3 those items to a dealer in the state they want to sell to.

Then at the state level, once the form 4 is done, that dealer can just drop your supressor in the mail and send it to you. If I bought a supressor from a dealer in Texas 6 hours drive away from me, I never need to step foot in their shop to complete the sale. I don't even have to leave home. They can just mail it to me because it is in the NFA.

Silencer Central either has an exclusive relationship with a single dealer in each state or they have registered themselves in each state so that the process is technically in house.

So they Form 3 (from the main manufacturer) to themselves (in whatever state), then Form 4, then mail it out to the consumer after approval.

That all stands to go away though. In theory you could (with the new system should it pass) go to the local sporting goods store and look at that cool new supressor in person, whip out the old AMEX, and go home with a supressor (after you do the 4473).