I'd assume some electrical supply dealer or online. Bulk LED strip is what's mentioned in that post...
Many a site popped up on a google search of Bulk LED strip and this looked like a good start if you want to just order them online
Edit: added reference to the referenced post
2013 F150 XTR 4X4 EcoBoost SCrew Blue Flame 157" - 3.73 MaxTow, Retro'd tow mirrors, Raptor 3rd brake light, Roll'N'Lock bed cover
Plans for AAL, new tires, more lights, HID retrofit
Last edited by Jeriko; 07-11-2014 at 12:21 AM.
Reason: adding reference