I use Tennessee Valley Bullets in So central Tenn.
http://www.tennesseevalleybullets.com/
and
Magnus in Huntsville Ala.
http://www.magnusbullets.com/
I would not worry about shooting .357" cast bullets in 9mm as long as the loaded rounds chambered freely. I shot .38 semiwadcutters in my P7 in moderate numbers without even leading up the gas cylinder.