You can leave it out, however, I do find it keeps them more crisp, especially later on. They are still good, no matter what ! The original recipe did not call for it.
I ordered some calcium chloride, food grade, of course online. Same thing as Pickle Crisp.
I got my Pickle Crisp at a local hardware store before.
It sells out really fast in the spring. You need to buy early if you want it in most areas. Very popular product.

I get it at Bulk Foods and its been a very good keeper.. The granule size is a little bigger than the PC product, so I add a small amount of extra to make up for the difference. I weighed a half teaspooon of PC and a HEAPING half teaspoon of Bulk Foods CC weighed the same.

Here is a link that might be useful: Bulk Foods CC