Hello, Blue88. Sorry to hear of your predicament. My first recommendation would be to look into clinical diagnosis to ensure you truly have IBS and not some other condition, or an infection of some sort. One common requirement for IBS diagnosis, for example, is pain. If you don't have routine gut pains, it's not IBS per the "Rome Criteria" (I'm commenting from memory here, but am pretty sure this is the case). Amoebiasis, giardiasis, candida overgrowth, and insufficiencies such as lowered pancreatic enzyme output can all mimic or exacerbate IBS, and most of these can also result in gas as well. See the link below.
Going by your spelling ("odour"), I'm guessing you're from "the other side of the pond?" My links refer to premier U.S. gastrointestinal labs, but you should be able to find UK or Australian counterparts by contacting several local alternative medicine doctors. For that matter, the U.S. labs I mentioned probably take international samples, I would guess.
Best wishes for your successful diagnosis and treatment!