You can get a repro Delco R-89 side terminal here.
http://www.antiqueautobattery.com
No one is manufacturing the Delco R-79 side terminal battery,which is what yours originally came with.They will sell you the Delco R-89 Battery,with the
"Correct Replacement for R-79" decal.That's as close as they'll get.
The R-89 side terminal was originally used in Vehicles begining in 1971 up.