You can find the Armaspec Sound Mitigation Buffer SMB Gen3 Carbine here. Fast $9.95 shipping! Orders over $200 ship for free!
The Armaspec Sound Mitigation Buffer SMB Gen3 is a self-contained, single-stage drop-in replacement for the buffer and spring. The Sound Mitigation Buffer prevents the buffer spring from rubbing against the buffer tube providing smooth, quiet operation. Made in the USA.

Buffer Weight: 3.3oz (Carbine)

The Sound Mitigation Buffer is available in 6 variations:

SMB-Carbine with a weight of 3.3oz SMB-H with a weight of 3.8oz SMB-H2 with a weight of 4.7oz SMB-H3 with a weight of 5.6oz SMB-AR10 with a weight of 4.7oz SMB-9 with a weight of 6.9oz