To the best of our knowledge, Lincoln Electric has obsoleted or has gone to "Made To Order", whatever that means, all the orginal SA DC exciter armatures. We will need a core, we have a few in stock that we can rewind. 
Normal "turn around time" after we receive you core is five to seven working days. All work is done in America, by Americans!
 
Is a short list of the steps we do to rewind the armature. Please note all the steps are done “by hand” we have no automated machines, expect for the winding isolation rotating fixture. This armature has been manufactured since the late 1930’s, it is a lost art.
 
The armature core is inspected for damage.
The original wires are removed and separated from the commutator
The core is baked in an oven overnight at 600’ F. This removes the original varnish.-
The original wires are removed, and their diameter is checked against the new windings
      to be reinstalled
Core is sandblasted, inspected, and clear coated with insulation.
Insulating strips are cut and installed in the slots. This adds an extra layer of insulation.
New windings are wound by hand and installed in the slots.
New holding wedges are installed to hold the windings in place.
Wires are soldered.
Commutator is machined to make sure brushes have perfectly flat contact.
Rotor is dipped in high temperature insulation and is submerges on a slowly
     rotating fixture, to assure through penetration of the liquid.
Baked to solidify the insulation.
Steps 11 and 12 are repeated.
Unit is tested for insulation integrity.
Final coat of red epoxy.