One can find a CableCARD on one's cable provider's website, such as Comcast or Time Warner. It is not possible to purchase CableCARDs elsewhere, as they are linked to a subscription.

One can get a CableCARD from Comcast by purchasing it at retail stores. It is activated by the retailer and provides TV services instead of purchasing an adapter and additional equipment.

You will need a CableCard-enabled device, of which many have recently started to trickle out.

Yes...TivoHD or Series 3 work with Fios Cablecards. You will need 2 Scards or 1 Mcard from Verizon.

Good question. Unfortunately, I'm not aware of any out there, but you could do a websearch for `cable converters`. You might find something there.