J&M (JMCB-2003) or Honda OEM are pretty much your choices. Keep a sharp and watchful eye on this site and eBay for if/when used versions of these radios come up for sale. New or used they do NOT come cheap!
I was looking at the same thing for my 03. The solution I finally found was far less expensive than locating and installing an OEM CB. A couple guys I ride with don't have the OEM, but want to communicate with the group, so they bought the Midland 75-822 portable 40 channel CB's. The radio gets clipped on their belt, add a wired ear bud with a push to talk button attached, and they talk with everyone. The upside, aside from the cost, is if or when they change bikes, the radio transfers along with them. The radios can be had for as little as $98, and the ear bud/mic/ PTT attachment can be had for around $14. Looking at OEM, you're into a radio for about $600 to $700, plus the antenna around another $100. Good luck and ride safe.