I don't know. If I knew I wouldn't be asking you guys, would I?.... My question stands, where are you going to find .450 conicals?
One diameter .44 cal round balls come in is .451 - if somebody's making conicals for .44 cal revolvers - and they are (but I don't know what diameters are available or who has them) - maybe those would work. Dunno. It's all a learning experience. Research ongoing. Partially here.
If it turns out I have to cast my own then the project is off. I'm way too far from being into that yet.