I have been trying to find this mythos pack since the beginning of last year. Does anyone know if it is out of print or when it will be back in stock. I have even looked at European sellers to no avail.

You'd be better posting this in the AH LCG forums. This is the AH board game forum...

https://community.fantasyflightgames.com/forum/512-arkham-horror-the-card-game/