Reddit reviews Tektro RX4.1 Reverse Aero Lever Set (Black)

That is one crazy ass setup you've got there! Here are some cheap bar end brake levers.

For what it's worth, bullhorns are generally only used on fixed gear or single speed bikes, precisely because of how your wonky stem shifters look. Unless you have downtube shifters or keep the thumb shifters on the bullhorns (which will still be painfully awkward to use), drop bars are the way to go.

You can use one of those levers that goes in the handlebar