I'm thinking about redoing my stock seats and would like to add adjustable headrests. Anyone know where to find the hardware to do this?

attached to a vintage recaro 914 seat - but that doesn't help you much.

Hmm the only idea that comes to mind is to retro-fit a set off another make of car. I recall a lot of japanese imports back in the 90's had adjustable head rest. And you could always have someone re-shape the head rest to your liking and recovered in the desire material and using the stock hardware from the donor car.