Allen, if you can not find the length you need maybe get a 'custom' cable made. I have had cables made (not for a Model A tho) by Gene at Flat-o products http://www.flat-o.com/accessories/speedcable.htm He may be able to help you out.
I'm sure there are others that make custom cables if you decide to go that route.
if you are close to any major city. there should be a speedometer shop that can make a cable for you. In our area it is Northwest Speedometer. in Tacoma