Trico makes a special flasher relay for LED's.
It's called EP-26 LED / 2-6 Lamps
You should be able to pick one up at your local Autozone, Checker, or Napa.
I think I paid around $17 for mine.
To be honest though, I don't like them.
I only used mine for about 2 days, then ripped in out.
It does take care of the fast flash, but it also causes a 1-2 second delay before the blinker starts to flash.
I just put up with the fast flash now.
Yes, it's a bit annoying, but it's also more responsive.
Hope this helps.