Stock Fiesta ST coils as well as the coils from the FR3 Handling pack are good and readily available.
H&R at one time offered two varients. Im not sure if they still offer what they refered to as the "Super Sport" version.
Eibach suspension has a couple of lowering coils sets available too.
If you decide to go with used coils don't overlook the Mazda 2 forums. That kit worked on the platform cousin of Fiesta as well. It was a bargain price that even the Mazda guys often couldn't resist. Some FR3 kits may come up for sale there. The springs are the thing. The FR3 struts and shocks are commodity grade at best even when new, junk after 15k.