NPD stopped handling them last year. Way to many returns from premature failures. They didn’t want to deal with it anymore.
http://www.concoursmustang.com/forum/index.php?topic=11672.0
You can do the wheelchair battery conversion if you have a 24F case to work with.
http://forums.vintage-mustang.com/vintage-mustang-forum/647191-best-battery-use-autolite-24f-case.html