Mine were some of the first Elise seats in a Miata, installed in 2009. If you google "elise seats in a miata" you're looking at my pix. ha! My blog slug is here: http://revlimiter.net/blog/category/miata/elise-seats/
Brackets made by a local shop. I have templates of the metal parts on my site. You can get them cut and welded to stock sliders by any local speed shop.
I restuffed them with Shocktec Air2gel foam and dissected the Probax foam. It's nothing special - open cell couch foam. The Air2gel is amazing. It transforms the seats.
(these are full of the new foam)
I also installed some shoulder slot grommets in my seats.