The belt itself is a black 5 cm leather plain leather belt. The belt buckle is permanently attached to the middle of the belt and I have the belt's own buckle in the back. It's never seen since it's under the vest anyway.
For the belt buckle I'm very grateful that Heather Tanner made a lot of research and posted this sketch on the Rebel Legion forums.
I printed it on paper and then cut it out in worbla.
To create the the two ridges I used narrow bands of worbla and formed them with my hands while they were still warm enough to be moldable. I also tried to smooth out the edges with my fingers.
The final step was to paint the whole buckle with silver spray paint.