If you're in Japan, you should be able to send it in to Cave. If not, contact tops-game.jp. It'll cost about 25,000 yen total to get the board fixed through them, provided they agree to be the middleman. It won't add that much to your board's value (the last fixed PCB sold for 40,000yen on YAJ, in other words, the going rate for the unfixed board), so only do it if you really want to save your scores on the PCB. You can unlock Ultra yourself, by the way (you don't need to send it to Cave to do this).
I have heard Cave no longer fixes Mushi PCBs, but as far as I know that's just a rumor. Give it a try.