Originally Posted by dddd

There were Shimano-branded road bars, but just like the stems they were made by Nitto.

I can't recall if Shimano-branded bars appeared below the Dura-Ace level however, none are common to find.

Shimano's aero stems were offered in both 25.4 and 26.0 clamping diameters.
I have found that Shimano's stems seem to easily fit over Cinelli 26.4mm bars in the a few cases I've tried, and relatedly that certain Ambrosio bars and stems are also sized at 26.4mm clamping diameter.