Making them yourself is also a good option. While it takes a bit of experience on a lathe, it is not that hard. I learned how to use a lathe when making my first silencer for a 300 whisper AR-15. There is nothing like the feeling of doing it yourself. Sort of like the feeling you get when you re-barrel a rifle, but twice as nice.
But there is a down side and I am not talking about waiting for the ATF form 1 (application to make and register a firearm) to be approved or the $200 tax that has to be paid. Even though the maker/owner of a silencer registered on an ATF form made the parts themselves, they can not replace any parts that might become damaged or lost in the future. The only exception to this is wipes, the rubber disks that some silencers use. They need to be replaced very few mags to stay in good working order, so it seems like a real pain in the butt.
The only way to legally replace parts on a form 1 silencer is to pay another tax, or send it to a SOT class 2 manufacturer and hope they will work on it. If I were to pay another $200 tax, I would rather make a whole new silencer instead of just replacing parts. The law is not very clear on this except to say that silencer parts are themselves silencers. The ATF has interpreted this to mean another tax has to be paid to make even one replacement part. It is a real drag in part because it means experimenting with new designs can be a very expensive proposition for the form 1 builder.
I am sort of getting around paying the $200 tax myself by making a few silencers for others who present me with an approved ATF form 1 so I can help them make it on the lathe for them, using my latest design.