I doubt you will ever see a mag kit from GW. They would rather have you buy more models.
I think they should, it would make them money
Because how many people actually do buy 4 tactical marine box sets for each combo?
They would rather buy some cheap magnets...
Through temptation and horror
I have held to my faith
As a drowning man grasps at a rock
Judge me not by my weakness
Remember not my sins of late