If you're looking for
Metacaulk® Fire Rated Putty Pads, which are ideal as wraparound seals of electrical boxes that not only seal the openings for sound attenuation but also provide
outstanding protection against the spread of fire, they are available at ebuildingproducts.com.
Access their home page and then follow the links to
Firestopping » Electrical » Metacaulk Putty Pads or
Firestopping » Electrical » Metacaulk Putty Sticks. (Sorry -- I'm unable to link directly to product page because the site uses frames.

)
Here's the
data sheet for both products.
xref: putty packs, electrical box sealant