If we’re including test prints, the two Matchprint Charizard comes to mind, with just two copies each:
From official releases only though, the unlimited edition Korean Base Set Charizard is up there, but I think the Thai 029/SV-P Charizard VMAX and Indonesian 039/SV-P Charizard VMAX takes the spot. Iirc, only 50 copies of each were rewarded:
Source: pictures from @rabby250’s collection, which he later graded as PSA-10s.
The Traditional Chinese 087/S-P Charizard VMAX HR with around 100 copies given out (although 500 announced by officials) is also an honorable mention:
Greetz,
Quuador