Test panels

I'm a bit curious what some of you have used for test panels or whatever? Such as figuring out what base to use an how much color to get the correct or closest matching result. Or if anybody knows where to find the metal bodies like in Eastwood, cause I think those would be real nice to show depth an shading.

With pearl and flake EVERY mix will turn out different. Just something to keep in mind.

That said I always have used a spare body panel.