I am really sorry you are having so much trouble with these sores. I have also had quite a few problems with ulcers since about 6 months ago. Mine are almost all on my tongue with the occasional one on my lip. I am also on remicade at the moment. It has definitely helped heal the ulcers quite a bit but they are still causing me trouble, and seem to be getting worse at the moment (coincidently my bowels seem to be getting worse recently as well, which I think is connected). I currently have a massive ulcer on my bottom lip for about the past 2 months, it is causing a little bit of swelling to the lip as well and making it a bit difficult to talk which I am quite self conscious about lol.
These ulcers could either be something else (e.g lack of certain vitamins etc)that has manifested itself because of crohns, or it could actually be crohns itself in the mouth. My doctor seems to think mine is the later unfortunately, I hope it is not the same for you. I assume you are already having regular blood tests, but if not it may be worth getting checked to see if you are deficient in any vitamins, which may be contributing to this.
Unfortunately there aren't many treatments available for mouth ulcers, the only treatments that are proven to actually heal them are benzydamine hydrochloride or buccal adhesive hydrocortisone tablets (neither worked for me). Other than that the rest of the things out there can only really numb the pain. Other than that I can only suggest that you basically use a whole variety of things at once in the hope that in combination they somehow help clear them up. In addition to the things already mentioned in this thread, people have claimed that vitamin b50 (which includes a number of different b vitamins), vitamin c/d, zinc, probiotics, l-lysine and hydrogen peroxide. Worth a shot I think as it can't do any harm anyway.
Btw I also discovered (and this is definitely scientifically proven) that toothpastes containing sodium lauryl sulfate in them can contribute to mouth ulcers. SLS is basically a detergent, and it causes irritation to the lining of the gums which can lead to ulcers. Not sure if it will help with ulcers from crohns but another thing worth a go. I don't know what toothpaste you have over there, but I know sensodyne is SLS free over here.
I hope you can find some relief soon. please keep us updated how you get on.