I'm in the process of redoing my seats in leather with a kit from 928 leather. I wondered the same thing about the foam and staples etc... Arrow makes a staple gun just like the classic T50 but with an attachment on the head that does the outward clinch. The model number is T-50-OC or T-50-OCp I ended up ordering mine online. I think it was around 40 bucks, but well worth it when you consider the cost of pro interior work.
It uses normal staples and you can adjust how much it splays the ends.
You will also need some high stregth upolstry glue for the down in the seams. Its not hard, just take your time and it will look good.
Here is one of the sections of the rear seats that I'm doing.
and the stapler
