Totally confused

Have a cat with IBS, vet recommended trying to eliminate an allergy to foul or fish
Impossible after hours of research and reading ingredients to find a food with lamb or rabbit that doesn't include chicken or turkey meal or foods that combine fish and rabbit or lamb
Anyone have any idea?

Nature's Variety has a Limited Ingredient Rabbit formula kibble. Rabbit meal and rabbit are the only protein source. The also have rabbit or lamb wet food. http://www.instinctpetfood.com/instinct-limited-ingredient-diets-for-cats

Orijen is a pretty expensive brand that uses mostly wild caught ingredients. 

Acana is another high end brand that uses multiple meats. I think two of their current formulas are foul free.

Since poultry is the cheaper protein any non poultry is going to be higher priced. 

Go homecooked or raw with EZcomplete.

http://www.foodfurlife.com/

http://www.rawfeedingforibdcats.org/

See the thread on novel proteins: http://www.thecatsite.com/t/306947/your-favorite-brands-of-novel-protein-canned-cat-food

You want to look for limited ingredient diets at the pet store. I don't think the chain pet stores have much of a selection so look in independent pet stores.

Are you looking for dry food or canned food? For canned foods, see the suggestions I posted here: http://www.thecatsite.com/t/327580/cat-food-flavors#post_4117421 Some of the rabbit and lamb foods for those brand don't contain other proteins.