You might find it difficult to get this because it's one of those items people generally won't have multiples of. They all farm SH Loki until they get it - and they then have no need to fight him anymore and therefore have no more GoM recipes to trade/give.
So go farm him is my advice (I know you didn't make this topic for advice
), but it's better than nothing when you have nobody selling GoM.
And just incase you didn't know, when farming loki on SH, (after you kill him the first time) you can change characters and it will reset Loki so you don't have to go through Asgard stuff all over again.
gl