This will give you a quick course on what you want. If you have a cage I would advise the FIA stuff. There is a little softer padding called holomagated(sp?) that is a combination of the sfi and the FIA. If you can't find it Google BSCI padding. Your head will thank you. Search here on the forum and you should find at least 1 or 2 threads about it.
Thanks Bill, however I think I need to do a better job of describing what I need. Roll bar padding is not quite what I was looking for (though I will still use it elsewhere...). I want the pad that goes behind the drivers helmet (think headrest). The photo below shows what I want; except that it clamps to the diagonal crossbar of the rollover protection in my car (as shown in the photo of my car in trailer).
If you run out of ideas for where to source the pads, you may have to make what you want. A good interior shop could knock it out for you. Some of the seat makers have helmet pads built into their seats, but that would be a high seat, which would change the look a lot.