Nope, not as far as I've seen.
I agree, the best solution is to have both DIN and yoke fittings to swap back and forth on your first stage. That's how we do it.
Other than that, the most common thing here in Europe and the Middle East -- where they've got dive travelers with both DIN and yoke regulators -- is to use 200-bar DIN valves that will accept a screw-in "donut" adapter for yoke regulators like
this... second one down... the valve is narrow enough so a yoke will fit around it, and has a dimple on the back of the valve for the yoke screw. Downside is, the insert takes a beating... and you have to worry about two exposed o-rings.
One issue with any adapter is that it has to be designed in a way that a yoke couldn't be connected to a 300-bar tank and valve, for which pressure it's not designed.
Theoretically, you could also use a fill adapter like
this... it screws into a DIN valve -- can only be attached to a 200-bar valve -- and a yoke can be attached to it. But the first stage would be at the wrong angle. Plus I don't think the fitting would have acceptable strength. I used one a couple times, many years ago.... but certainly wouldn't recommend it now.
Kind of like one of the standard questions at the Army Armor Officer's Basic Course in the mid-70's... "Can you fire the M-551 Sheridan's 152mm main gun while the vehicle is swimming?"
"Yes. Once."
--Marek