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There's a 135 mm option from Mack.
https://mackhubs.com/hubs/track/high-flange-rear-iso/
Disc mount on both sides, maybe he'll make some custom end caps to make it compatible with the 142 mm spacing you need.Edit: Forgot about this one:
https://www.effigear.com/en/119-moyeu-arriere-roue-libre-14812.html
Don't know if that's really a thing or not though...
Think they've pushed out the delivery date since the last time I visited the website.
Could work. Would quite like to use both brakes. Ideally it would be 12 x 142 and have two ISO disc mounts, but that's quite a niche.