You can find someone to make you (modify) a .357 SIG barrel for your P07/P09, Tactical Sport, etc. but it will cost you.
I guess there wasn't (isn't) enough demand for it from the companies that make .357 SIG barrels.
I found a .357 SIG barrel for the FNS .40 4" and had to wait a couple/three months for it till they got enough orders to make it worth making a few.
Same company didn't offer CZ .357 SIG barrels.
.357 SIG? .40 S&W? 9MM? Like the Ford, Chevy, Dodge lover arguments. Nothing is perfect and people will always find a reason to choose one over the other and be able to argue why their choice is better.
I always get a kick out of people who say you don't need the extra velocity of the .357 SIG and then turn around and promote 9MM +P ammo because (wait for it) of the additional velocity.
If it's true (born out by street shooting results) the 9MM will stay the king of the street. Not sure if the videos of LEOs shooting people till the slide locks back are the norm for OIS these days or not. If so, will it begin to upset a lot of people that LEOs are shooting people so many times? I don't know.