Scraped from Wowhead.
Since Wow does not provide an API like GetName() for NPCs in WowClassic, these are manual tables for NPC names.
Add these lines to the top level of your .toc file.
## Interface: ~
PathToYourLib/NPCs/id_to_npc_classic_en.lua
PathToYourLib/NPCs/npc_to_id_classic_en.lua
PathToYourLib/NPCs/id_to_npc_classic_cn.lua
PathToYourLib/NPCs/npc_to_id_classic_cn.lua
PathToYourLib/NPCs/id_to_npc_classic_de.lua
PathToYourLib/NPCs/npc_to_id_classic_de.lua
PathToYourLib/NPCs/id_to_npc_classic_es.lua
PathToYourLib/NPCs/npc_to_id_classic_es.lua
PathToYourLib/NPCs/id_to_npc_classic_fr.lua
PathToYourLib/NPCs/npc_to_id_classic_fr.lua
PathToYourLib/NPCs/id_to_npc_classic_it.lua
PathToYourLib/NPCs/npc_to_id_classic_it.lua
PathToYourLib/NPCs/id_to_npc_classic_ko.lua
PathToYourLib/NPCs/npc_to_id_classic_ko.lua
PathToYourLib/NPCs/id_to_npc_classic_pt.lua
PathToYourLib/NPCs/npc_to_id_classic_pt.lua
PathToYourLib/NPCs/id_to_npc_classic_ru.lua
PathToYourLib/NPCs/npc_to_id_classic_ru.lua
PathToYourLib/NPCs/table_localization.lua
...
Get your classic NPC table like this in your main addon
localeCode = GetLocale()
id_to_npc = ClassicNPCTables:getDataByLocale(localeCode, "id_to_npc")
npc_to_id = ClassicNPCTables:getDataByLocale(localeCode, "npc_to_id")
These all tables takes 0.000125secs to load as I tested on my PC, which is no big deal at all.
Of course, it would be different from PC to PC, but I think loading tables of this size is no big deal.