http://www.thepartsplaceinc.com/ocatalog/part.asp?VID=7&YearList=1972&Search_Keyword=cable Part # AT5557S
Last time I checked most parts stores carried a whole host of kick down cables on the shelf. Most for $20 or less, though it's been a long while since I priced them.
Maybe so, but the Buick one connects to the gas pedal unlike the Chevy one (which I am sure is readily available)