How can I summon a villager that sells spawners for mobs other than the default Pig?

Question

I've tried A LOT of different syntaxes and nothing has allowed me to reach my goal. I want to create a Villager that A) sells spawners (I've been able to do this) and B) have those spawners spawn mobs other than pigs. So like a zombie or something. From there I could name him a "Zombie Spawner Trader" or something like that. Keep in mind, my villager is being created no problem and he's buying and selling things according to what I've programmed, all that's wrong is that the spawner is only spawning pigs. I have tried NBT tags: "Entity", "EntityId" and "SpawnData" with their proper syntaxes according to the wiki, and none of them worked. It proceeded to give me a pig spawner as usual.

Some code:

/summon villager ~ ~1 ~ {CustomName:"Zombie Spawner Merchant",CustomNameVisible:1b,NoAI:1b,Invulnerable:1b,Offers:{Recipes:[{buy:{id:"minecraft:gold_nugget",tag:{display:{Name:"Gold Coin",Lore:["$1"]}},Count:32},sell:{id:"minecraft:mob_spawner",Count:15,tag:{SpawnData:{id:"minecraft:zombie"}}}]}}

Answer 1

This command will summon villager that will trade 32 coins for two zombie spawn eggs. It will also trade 1 zombie spawn egg for a monster spawner. The player can then combine the two to make a zombie spawner.

/summon villager ~ ~1 ~ {Invulnerable:1b,CustomName:"Zombie Spawner Merchant",CustomNameVisible:1b,NoAI:1b,CareerLevel:1,Offers:{Recipes:[{buy:{id:"minecraft:spawn_egg",Count:1b,tag:{CanPlaceOn:["minecraft:mob_spawner"],EntityTag:{id:"minecraft:zombie"}}},sell:{id:"minecraft:mob_spawner",Count:15b}},{buy:{id:"minecraft:gold_nugget",Count:32b,tag:{display:{Name:"Gold Coin",Lore:["$1"]}}},sell:{id:"minecraft:spawn_egg",Count:2b,tag:{CanPlaceOn:["minecraft:mob_spawner"],EntityTag:{id:"minecraft:zombie"}}}}]}}

Its a bit hacky I know, but I'm pretty sure that villagers wont trade for custom spawners.