As far as buying a flasher unit to support LED is hard to find but I can say use the load resistor with a quick connect/t-splice to connect it.
I use LED switchback and use a quick connect. Easily able to remove the splice to go back to factory
2013 Ford Focus BOOS[ST]ED
2010 Ford Focus "S"edan (11 Psi, GT28RS) - Sold
ROTM Nov '11 (2010 Focus S)