I don’t know how many of the retailers sell the AS-PC2 cables but I know that you can get them through the Humminbird Customer Resource folks (1-800-633-1468) if you are here in the U.S.
Be aware though that these were meant to be used with the smaller units, so if you are going to use them with 987 or 1197 series unit; you will have to figure out a better means of powering the unit. Many will cut off the battery holder and connect it up to a rechargeable 12 volt battery to use while updating the unit.