Reddit reviews Tektro RX 4.1 Reverse Brake Lever Set Blacká

These work great for these types of bars and are dirt cheap.

Time Trial Levers. The Tektro RX 4.1 is my favorite.

Uh, I believe you just get the normal like this. Then you get an interrupter lever like this, and boom. Levers in both places. Not claiming to be smarter than anyone. Just surprised no one had suggested it. You don't have to get the levers I listed, just the same "type" I guess.

Yes, it's possible to do all sorts of bodges and have them work. Personally, I'd just buy a proper set of brake levers. They're generally not that expensive. A pair of Tektro bar end levers is about $20.

pretty much. They give you the drop bar hoods and ramps positions, and they're slightly cheaper to convert to.

Consider something like these TT levers as a cheap brake lever swap. Depending on how your shifter(s) is/are set up, that might take some more finagling.

I converted an old rigid mtb to a bullhorn commuter and rode it happily for years.

If you find yourself there a lot, there are brake levers that mount on the ends. I'm planning on getting a set of those once I convert a used single-speed I have to bullhorn bars.

I want to put bullhorns on my Specialized Sirrus SS. Does that make sense for the geometry? Also I would want to put the tektro rx4.1 levers on the ends. Would that work with my v-brakes?

https://www.specialized.com/us/en/sirrus-single-speed-mens-spec/p/173615?color=271962-173615

Tektro RX 4.1 Reverse Brake Lever Set Blacká https://www.amazon.com/dp/B001CJX4WO/ref=cm_sw_r_cp_api_i_5RyFDbNPB1V6Z

When you check amazon for these levers it also lists what other people have bought with these levers.

You could try to buy one of those, or contact a webshop/lbs regarding the inner diameter.

Actually I think those levers might have a smaller diameter because they're made for aero bars... not sure. But these look good:
tektro bar end reverse brakes, Dia Compe

https://www.amazon.com/Tektro-RX-Reverse-Brake-Blacká/dp/B001CJX4WO

I have these on my Origin8 Bullhorn I

Perhaps Tektro or Dia Compe. I've used Tektro in the past, they're great.

Edit: I've used both of these on different bikes

Velo Orange also sells a pair I've used on Nitto Northroad bars: http://store.velo-orange.com/index.php/dia-compe-inverse-brake-levers-22-2.html

Tektro: I use these on bullhorn bars like pictured in OP photo: http://www.amazon.com/Tektro-RX-Reverse-Brake-Levers/dp/B001CJX4WO/191-0082638-2564130?ie=UTF8&*Version*=1&*entries*=0