Singlespeed & Fixed Gear - Brakes for bullhorn handlebars

I have a bullhorn handlebar for my fixed gear bike which was cut from a dropbar. I want to install brakes but I don't want those bar end type. I would like to put it in the straight part of the bullhorn. Will the ordinary brake levers like from those from mountain bikes and BMX fit the bullhorn handlebar? Or are those different kinds of brake levers?

Usually people use cross levers like these (http://www.retro-gression.com/product/tektro-rl720-721-cross-levers), but anything that has the right diameter should work.

I have tried MTB brakes but they don't fit :(

Again, the most important thing will be the spec'ed diameter. If you can you should measure the diameter of the bars where you want to put the brake.

any lever with a hinged clamp is a bonus. do you want to, say, unwrap a bar just to swap a brake lever? or swap bars (get a proper bullhorn, flop&chops are short on reach, and though i hated my origin8 when i got it, now i like stretching out to the tip of the bar).

Like Prooftheory said (and linked) - any cross lever will work with the right diameter of the bar. In my experience, you need to either get dawn dish soap or any other biodegradable lubricant to help slide the brake on without scoring the hell out of nice, shiny bars. Hinged works better.

My Soma El Toro has been binned after riding on it for 2 months because I found that I liked having more hand positions; went with a Nitto Noodle and the conversion is where I learned about the scoring issue with installing, uninstalling the brake levers.

In my experience cross levers are often sold at either 26.0mm or 31.8mm with an included 24.4 shim, the second option looks kind of jankey when shimmed in my opinion but it's affordable and versatile if you switch bars later since 31.8 can be shimmed down to pretty much anything.

Personally I'd measure and get the right one, though, it just looks cleaner. Use a (metric) ruler and measure how wide your bar is at the point you want to mount the brake. 26.0mm seems to be less common except in cases where the part the stem is mounted to extends out and you want to mount it as close to the center of your bars as possible (I have to use one to mount to the center of my Nitto RB-021s).

I guess, what bars do you have? Can you post a photograph? Do you know your stem clamp diameter? It's often pretty easy to guess your bar diameter from that if you don't have the ability to measure it.

Anyway Tektro, Origin8, and Soma make affordable ones in every size (that clamp on so you don't need to rewrap your bars to put it on), I bought a Paul one because I liked it and had some extra cash at the time.