Floyds only come in 10". I believe the gotoh/Ibanez style locknuts are 16". I have no idea why they don't make a 12" as it's probably the most popular fretboard radius.
I've used the 10" radius nut on many guitars, from everything from Fender Strats, to Gibsons, and everything in between. It's fine.
I absolutely guarantee you, that you won't even notice. Not to mention the fact that the Floyd itself has a 10" radius, anyway.
Why not a Kahler locking nut? Keep the original LP nut in place and just add their locking device behind the nut?