I cut my drop bars and flipped them to use as bullhorns. Now I want to go back to drops but I can't find a new drops that are installed by "threading" them through the stem. By threading I mean the type which has a thinner bend at one side so you can install it without removing any screws. What are my options?
Most modern stems are of the type you're looking for, ie. with a removable front plate so bars can be switched with levers attached. The bars don't factor into this at all except that the center diameter must match the stem clamp. Current production is mostly 31.8mm, but there is still 26mm (old road bar standard) and 25.4mm (mtn bars and many Japanese road bars).
If you have the stem, verify the clamp diameter, and shop for bars accordingly.