I haven't seen any advertised, that doesn't mean they don't exist, I just haven't seen any. It's like Douglas says, most make their own.
In the next week or so I will be making a few sets myself so it would not be a problem to whip up an extra, if you cannot find some else where.
I will be using ash, mortis and tenon joinery and a seat size approx. 8 1/2" X 12 1/2"
I like to use a bit tighter (5/8" hole spacing) weave than what Douglas recommends but it makes no difference. It's just what I'm used to from past chair re-caning.
If you cannot find what you are looking for or don't want to make your own, let me know and we'll set you up with a set of seats....cheap!