If a person lives in AL, AR, AK, AZ, CO, CT, FL, GA, ID, IN, KS, KY, LA, ME, MD, MS, MT, NE, ND, NV, NH, NM, NC, OH, OK, OR, PA, SC, SD, TN, TX, UT, VA, WA, WV, WI, or WY then they can own a silencer without a license, just pay the $200 tax on the ATF form 1 or 4.
Take a look here;
http://www.silencertests.com/links.htm for links to manufacturers and other info. The forums on
http://www.subguns.com and
http://www.silencertalk.com are other good sources of info, especially for law summaries and making your own silencers. 308 silencers are not nearly as common as those for the 223 remington, but are not rare as silencers go. As long as you are shooting out in the open a suppressed 308 can be safe to shoot without ear plugs even when using supersonic ammo.
Ranb