All depends on the wheels you have. You can make anything fit. Just need wheels big enough to fit over them. Mine are 911 turbo calipers, but need 19" wheels to cover them
 
Boxter fit, so do some 911. you'll need custom brackets and not porsche discs, think awesome do a kit but you can makie them up yourself to.
Guy i used to know had porsche calipers on his 106GTI - talk about over kill!
 
Have a look at ECS - They are a US Company that do seriously BIG Porsche brake Conversions for Mk4 Golfs.... And the Golf's have practically the same setup as a Leon, so they should fit your car :)

http://www.ecstuning.com/

There are also a few UK company's that sell ECS kits.....

Jabba also offer a Cayenne 6 pot conversion with 356mm disks etc... But you're looking at - at least £1500ish
 
I think you would have to get the holes professionally re drilled from a proper milling machine or find alternative disks from red dot or somewhere.
 
Awesome do the boxster kit (mounts and brake lines) for 230inc vat, then you could get boxster calipers from a scrappy and your probably looking at 80 for a set of 312mm discs.

or but the whole kit for 750ish iirc.
 
I loked into the ECS kits and the only one worth going for is the stage 5 ( chayane ) as all the others have very small pots ( i think the 2v2 kit uses a rear boxter callaper ) and it was better to go for the brembo gt kits and are alot cheaper.
 
i have found the mounting kit on the Awesome website but it says that its only for Boxster caliper. Found some tatty boxter calipers for 165 so would work out less than 400 for the bits I suppose