Re: Tuning machine question.
I know for sure Schaller makes at least the M6 locking tuners with a 3+3 option. Heck they even make 4+2 for MM's etc.
If you're from USA, check no further than Stew-Mac, they are official Schaller dealer with replacement parts and everything, if they don't have it, no one does. Maybe a bit pricey and shipping isn't forgiving too, but at least you know what you're getting.