Originally Posted by JohnDThompson

Looks like a Simplex front derailleur mount:



The bad news is that these braze-on Simplex front derailleurs are not common, so be patient. The good news is that if you find one, they are actually quite good derailluers.

N.B. [MENTION=35857]oldbobcat[/MENTION] has a point: it does look pretty high for a front derailleur mount, but as he notes, it may be possible to mount a standard front derailleur below that.