You might look for it as "Pickling Salt", which is the same thing....some larger supermarkets should carry this. As far as Kosher being used as a substitute, that may be possible:
"Kosher salt is preferred over table salt for canning and pickling. Like pickling salt, kosher salt is free of iodine, which can react adversely with certain foods. Some brands of kosher salt contain yellow prussiate of soda, an anti-caking agent, but unlike the anti-caking additive in table salt, it doesn't cloud pickling liquids."
So you might want to check the Kosher brands to find one that does not contain additives....
Hope that helps,