In preparation for picking up my new Gemtech, I was nosing around their website and reading their FAQ's (added the bold myself):

Can I order replacement parts from Gemtech?
No. Silencer parts are tightly controlled by the BATFE and individuals may not possess spare or replacement parts. Baffles, spacers, end caps, tubes, or other components deemed to be suppressor parts by BATFE cannot be sold to individuals or even other Class III dealers or Class II manufacturers. We can however, repair, replace, or upgrade every part of your suppressor except the serialized tube; but the suppressor must be sent in to Gemtech and damaged parts are destroyed in the process and not returned.