I posted a thread a while ago looking for someone who was willing to RGB mod my Duo-RX. While cjameslv made a very kind offer and was a pleasure to exchange emails with, I live in Japan, and he's in America. The shipping costs would have been insane.
I went on Yahoo auctions and found a seller by the handle "ez0ya". You can find him by searching for "RGB 改造" and clicking on one of his Famicom auctions. With a polite message or two, I managed to get him to agree to mod both of my Duo-RXs and throw in SCART cables for each for 10,000 yen apiece. He even made me an otherwise unavailable adapter cable (SCART to AV multi; no more converting to component for me!) for a reasonable extra fee.
It felt a little scary sending my stuff off to a random guy I knew almost nothing about, but in less than a week, he had modded both systems and returned them to me. His work is clean and tight, as far as my amateur eye can tell anyway, and the resulting picture is beautiful. Even his packaging was downright professional. I can't recommend him enough.
He doesn't seem to speak English, though. However, if you want to get in touch with him, I can help you.
That's all, folks!