How Can I Get These Parts Bright White?

I'm working on the Italeri 1/72 scale model of the XB-70 Valkyrie. I've never worked on a model this large before and I'm having trouble getting the body to match the color of the real world aircraft.

I've given it two coats of white primer, followed by two entire cans of base white and pure white tamiya spray paint. All it's done is make the parts a shade or two lighter gray than how they are off the sprues.

Is there a different kind of paint I can use that will get a proper bright white coat on these parts? Or do I just have to keep buying can after can of white Tamiya until it's got two dozens coats on it?

I'm working on the Italeri 1/72 scale model of the XB-70 Valkyrie. I've never worked on a model this large before and I'm having trouble getting the body to match the color of the real world aircraft.

I've given it two coats of white primer, followed by two entire cans of base white and pure white tamiya spray paint. All it's done is make the parts a shade or two lighter gray than how they are off the sprues.

Is there a different kind of paint I can use that will get a proper bright white coat on these parts? Or do I just have to keep buying can after can of white Tamiya until it's got two dozens coats on it?