This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
From our Thomas Jefferson of rec.food.preserving, Paul Hinrichs
Both the Sausage Maker (1-716-876-5521) and Stuffer's Supply Company
(1-800- 615-4474) sell beef and lamb casings. I am not aware of the
slaughtering requirements for a casing to be deemed "kosher", but if all
that is needed is for the product to be free of blood, then these will pass.
You might also check the Con Yeager Spice Company, who I've been told have
very reasonable prices. I don't have their number, but I believe their web-
site is http://www.nauticom.net/w-pa/yeager.htm. It shows mainly spices for
sausage making, but you can get a list of stuff available mail order by
calling 1-800-222-2460 or faxing 1-412-452-6171.