I buy cheese making supplies online from The New England Cheesemaking Co. Since you mention you keep Kosher, you might be interested in the vegetarian rennet (tablets or liquid) http://www.cheesemaking.com/cheeserennets.html
In my cheese making, I have found the age of the milk, and whether it has been pasturized commercially at quite high temperatures has made a lot of difference. Since I live in Hong Kong, where it is hard to get milk that has not been pasturized at very high temperatures, I mostly make soft cheeses. I have only been successful w/ mozarella once or twice.
Good luck & have fun w/ your cheese making.