Oooooh, Pennywise. I've been playing some of your fan-translations recently. Nice work.
As for a similar mapper, yes, I was hoping to find one that allowed the game to run without crashing. I followed this:
It is to the ordinary Namco 108 family boards (mapper 206) as TKSROM and TLSROM (mapper 118) is to ordinary MMC3 boards. Instead of having hardwired mirroring like mapper 206, it has CHR A15 directly controlling CIRAM A10, just as CHR A17 controls CIRAM A10 on TxSROM. Only horizontal mirroring and 1-screen mirroring are possible because the Namco 108 lacks the C bit of MMC3. Disch's older notes described an extended and mistaken version of this mapper with a full MMC3, so some emulators may be doing it that way. That extended version is identical to mapper 118, except CHR A15 (bank bit 5) controls CIRAM A10 instead of CHR A17 (bank bit 7).
I can't recall which one it was now... There's a whole bunch of different Namco specific mappers. But I was screwing around editing the iNES header on Dragon Buster and making it try to run under different mappers and one of them loaded the caverns, and you could play it, but the status bar was full of garbled sprites. Which is at least better than it crashing at the start. Then I got bored and stopped experimenting.