Belinda's Greatsword Skin
No one ever knows when something will come back, only when it last did — which in the GS’ case was in the last week or so.
The next likely time (which is not the only possible time, or guaranteed to happen) will be in August during any anniversary sale they have for the game’s 5th year. Or possibly if Marjory figures more hugely in the next LS episode and her ghostly sword comes into play, ANet will sell to players at that time.
I’m sorry you missed it. That hurts. For the future, gw2timer.com uses the API to watch for things returning to the gemstore and can alert you; I wouldn’t be shocked if one of the mobile applications for gw2 offers a similar feature by now?