I just looked at the link you provided and realized I misread your statement. I thought you were saying all nigari is from China. Call it a blond moment.
I have only ordered the nigari and also the Masu (liquid nigari on the page), but I haven't used it yet. With shipping, it ends up costing me around $20 for two 5 pound bags of the nigari. I think the longest it has taken for my order to arrive is 3 days. Pretty quick. I haven't tried other brands of nigari, so I don't know if there is a difference. There's an Asian grocery store close to where I work, so I may check there the next time I need some. I ordered 20 pounds in my last order, so it might be a little while before I need to buy some more.