Here’s a link to a well established and well documented elemental formula, Vivonex: http://www.nestle-nutrition.com/Products/Product.aspx?ProductId=a3bc4b10-3701-4020-9742-d947a30ed612
You will also find a link to purchase it on the page. All the elemental formulas tend to be quite expensive, but this used to be the one of the best bargains, at least comparatively speaking, because it comes in packets that you mix yourself with water rather than in bottles. However, I don’t know if the pricing has changed. It was made by Novartis Nutrition, which was acquired by Nestlé Nutrition last year, so there may have been adjustments. Nestlé nutrition also makes Peptamen, a semi-elemental formula (http://www.nestle-nutrition.com/Products/Product.aspx?ProductId=d17ba8f2-6b9a-43c4-b683-55d0e590388f), and also some polymeric formulas, including Nutren, which Ilini mentioned to you. Many people do find that Ensure or Ensure Plus (both our polymeric formulas) work for them, so that’s another option, especially if you are on a budget. Your insurance company might cover the cost of total enteral nutrition for Crohn’s, because it’s a treatment that has been clinically tested and shown to be effective, but it depends where you live.
Regarding your request for more information, these elemental, semi-elemental, and polymeric formulas (referred to collectively as enteral nutrition), are an old treatment for Crohn’s disease that can still be very effective. They are liquid diets used instead of other food and beverages, usually for 2 to 8 weeks to induce remission. Some people also use them to maintain remission (using around 750 calories per day of the formula in addition to a regular diet). There are a bunch of different formulas, and they all seem to work about the same, but some people will respond to one type of formula and not another (not predictable in advance, it’s trial and error). Doesn't work for everyone, but generally you will see improvement within 10 days if you are going to respond, so you don't have to stick it out too long if it's not working. They will sometimes work in people who do not respond to steroids. The formulas provide all the nutrients you need in a day, so as long as your husband drinks enough of the formula (say, 2000 calories per day, or more if necessary depending on his size and activity level), he will not be hungry and will not lose weight. He can drink extra formula if he needs to gain weight.
Anyway, I hope that helps.