TM Soundproofing direct has free shipping, also available on Amazon Prime (where i order mine from).
If you need something thinner (but more expensive) you can use 1/64" thick sheet lead for the same effectiveness (1lb per sq ft). Roto Metals.
yeah, i have 1/16" thick in my footwells along with mlv, cld, and ccf to cut tactile feedback (see my build log for details)