You'll have a tough time finding road stems with more than a 20-degree drop. You might find something designed for a big rise (modern equivalent of Nitto's DirtDrop stem) and then just flip it, but with too much drop you might bump into the headset itself, and need an extra spacer to make room, and thus the spacer will nullify any gains in the drop of the handlebar.
__________________
"c" is not a unit that measures tire width