stuck and rust spark plug

All good ideas here, the thing that you have going for you is the head is off.
Clean everything around the plug on both sides.
Since you cannot purchase Aero-Krol.

Heat the area around the plug, (try to avoid heating the plug, you want to heat the area around it to expand the metal), on the combustion side with a torch, add candle wax, gently tighten / loosen until it screws out.

If it is still stubborn keep heating and adding wax, you may have to let it cool down to room temperature and do this several times but it will remove a fastener.