You might try a Vela flash, here is their blurb:
http://www.vela.io/vela-one-high-speed-flash:" VELA ONE HIGH SPEED FLASH
VELA POP HIGH SPEED SOUND TRIGGER
Vela One: The fastest flash in the world
The Vela One is the fastest flash you can buy. Take pin-sharp photos of supersonic bullets and explosions using a normal SLR. The pulse width is adjustable between 500ns (1/2,000,000 sec) and 5µs (1/200,000 sec), which is fast enough to freeze a high velocity rifle bullet in flight.
Your flash is too slow. High speed photography relies on a fast flash. Just like shutter speed with action photography, it's the duration of the flash that is important when capturing bullets and explosions. A typical speedlight has a duration of around 1/20,000 second (50 microseconds) on its fastest setting. This may sound fast, but a bullet will travel over 5cm or two inches in that time and will be so blurred it's almost invisible. Studio flashes are even slower. For pin-sharp shots you need a much faster flash, and the Vela One is 100 times faster. With a flash speed starting at 1/2,000,000 second, or 500 nanoseconds, the Vela One will stop a supersonic, high velocity rifle bullet in its tracks.
WHAT'S WRONG WITH HIGH-SPEED PHOTOGRAPHY
We've all seen the beautiful high speed shots of bullets passing through playing cards and apples. If you want to take these sort of photos today, you will either need a high speed camera costing tens of thousands of dollars, or a dangerous and expensive air gap flash. These use a high voltage spark to generate the short, bright flash needed. As they run at over 25,000 volts and need regular and dangerous electrode replacement, it's not surprising you can't buy them commercially. If you want one you either need to buy a vintage one for thousands of dollars, or you must build one yourself. Many super talented people have done this, but it's not an option for most of us. We wanted to solve this.
THE VELA SOLUTION: A MILLION LUMENS
To solve the problem we turned to LEDs. Until now this has been impossible, as high speed flashes need to be extremely bright in order to get enough light onto your sensor in such a short period. We worked out we'd need to aim for up to one million lumens. If we used regular ultra-bright (500lm) LEDs we would need around 2000 to achieve this. This is obviously far too expensive and impractical. Instead we turned to the latest "chip-on-board" LEDs. These are designed for for applications such as exterior lighting of large buildings. Even at ten times the brightness of the regular LEDs we'd need 200 of them, which is still far too expensive and impractical. This is where we had to get clever. After months of experimenting with different circuits and LEDs, we have built a circuit that drives nine LEDs up to 20 times brighter than rated, without damaging them or overheating, pumping out up to one million lumens. We've flashed our test units hundreds of thousands of times, and they power on through. That's years of normal use, and far longer than a speedlight will last."
The great photos of apples + speeding bullets make downloading the Vela web page worthwhile. I was unable to copy them here.