Here's the handbook text:

In addition, effective January 1, 2009, the boat shall include a nominal 4.8 cubic feet of buoyancy to facilitate the rescue of a swamped boat. This buoyancy shall be composed of a choice of an air bag, rigid non- communicating air cell foam plastics or air tanks and shall be attached inside the hull at the bow as low and far forward as possible to provide a nominal 300 pounds of buoyancy when submerged in water. It shall be securely fastened so as not to become dislodged when submerged. (November 2007) (See also CMR #29 & 79) 

Here's the kit on Flying Scot Inc Store:

Bow bag kit with cover480130
4.54 lbs
 
$ 196.80 

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Includes the bag, protective cover and all parts required for installation. (As per current new boat installation)

There's also one at APS on this page:
http://www.apsltd.com/c-3014-flying-scot-hardware-and-accessories.aspx