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.
Mack has the same mounting face spacing as the 110×20 hubs, lines up with track cranks but not brakes.
Effigear seems to be an aluminium HG spline cut straight into the hub shell, there's no way I'd use that. Even a threaded sprocket would be better.
What about a wide foot sprocket? Should in theory prevent the sprocket from digging into the softer spline...
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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.