In addition to the points Alex S made, you need to consider why they want RAW. There are several possible reasons:

• Bit depth as Alex S said.
• JPG suffers from compression artefacts which RAW doesn't. Blown up to exhibtion size these can jump out and ruin a print.
• Having the RAW file is often used as a proxy for having taken the photo, as RAWs aren't generally published. This is to avoid cheating by submitting someone else's image. TIFF and other formats support high bit depth without lossy compression and are used for distribution of high-res images, so the only reason to have the RAW is that you shot the photo.
• It's possible they want the as-shot image, though that's unlikely to be for display. Post-processing is part of the digital workflow, and the question is more one of how much is acceptable. Having the RAW file gives them the ability to check how much you've modified the image. I've seen RAW+TIFF submission requirements explicitly for this reason.

So you're probably out of luck this time. I (as an amateur) almost always shoot RAW+JPEG, as many of my shots are just printed with at most a little cropping, but some need proper work. This (if it's an option on your camera) may be an option in the future.

It is possible, if this is a local competition, that they've just copied the rule from somewhere else, so it might be worth getting in touch with them.