Are you picky about rise angle and clamp diameter? There are lots of MTB and hybrid stems out there that are similar. Most are going to have an extension with rise and will have a 25.4 clamp. Plenty of 25.4 drop bars exist, so the clamp diameter is not a big deal if you're not picky about the handlebar. Some clamps will be too wide to thread a drop bar through, so you may have to remove some clamp material. I used a Tioga T-Bone on one of my touring bikes without modification. Nitto made the Technomic with a through cable but most Technomics won't have the feature. Might be worth looking through the Nitto catalog though - they have tons of stuff that you don't often see.
Here's my 1985 ST500 with the T-Bone.