Brettuns Village Leather (brettunsvillage.com/leather) is a good, if unpredictable source for armor leather, too. They don't seem to have "armor sides" in stock right now, but they sometimes do. They do have some sole bends in stock, but they don't list thickness (which they're usually good about). Depending how much of a hurry you're in, it might be worth contacting them; their prices tend to be better than the more predictable places'.
Edit: They do have skirting scraps (
http://www.brettunsvillage.com/leather/scrap/scraps.htm about a quarter of the way down) which is 14 to 16 oz, but odd bits and pieces (I got a box of this stuff a few years back--most of it was useful for small things, like brig plates, and some was big enough for things like shoe soles; none was much bigger than that, though).
Anyway, hope that helps!