If you really want semi-elemental/elemental, you may be able to find them at drug stores or a medical supply store. Otherwise--online/Ebay but you will pay a lot for shipping. If you can find the book by Jini Patel Thomson she discusses how to make it from scratch and sells a product called "Absorb Plus" but it is expensive.
You don't really need to use such a formula, polymeric ones work the same, taste much better, and cost a lot less. I can tell you this from personal experience. I have lived off a polymeric formula for months but can barely get through half a can of Peptamen (semi-e) it's that awful.
Something like Boost, Ensure or Ensure Plus, and there are generic versions of those two. There are also higher-fat versions, I personally have used Nutren...maybe you can find that at a medical supply store or a hospital pharmacy.
July 2007 Drug-Induced Liver Injury
January 2008 Crohn's Ileitis
Entocort, Enteral Nutrition, Omega-3 (Flax Oil and Fish Oil), VSL#3, Vitamin E