Once again, there is always New Moon’s Klingon department
, which features three styles of belt buckle including the TOS standard.
Of course, there is always the bubble-wrap-spray-painted-with-metalic-paint approach. I don’t think such a thing would last long, but would serve you well in the short term. Being cheap and easy to produce, I suspect that they only had to last as long as it took to film one scene.
Beware that a solid metal buckle is going to be difficult to produce and heavy to wear. You may find it tugging the rest of your costume out of place. Also, in choosing belt buckle materials, ask yourself, “How much time and money and potential injury do I want to put in to what is a relatively minor part of a very detailed costume?"
zero g has come up with some techniques for both the TOS
The original I sculpted out of clay around which I poured latex to make a mould for casting resin. The resulting piece had pre-planned hemispherical cavities which I filled with iridescent marbles. The back has steel clips embedded in it to take the belt.
I sculpted the baseplate in clay upon which I arranged little plaster hemispheres previously cast in an ice 'cube' tray. The whole positive was then moulded in plaster, and a fibre glass resin piece pulled from that. I wasn't worried about reproducing the item and destroyed the mould getting the accessory out.
belt-buckle styles. There is no reason you could not switch the techniques and styles around. The TOS variant looks much sturdier but involves more work. Is it worth it to you to sign up for a flickr account to contact him and ask if he will discuss the details?
If you’re pressed for time and don’t have time for smithing or fighting with fibreglass, you could also go the Sculpey route. Cut a slice off of the brick and flatten it into a the desired polygonal shape. Flat spatulas are good for getting even edges and thickness. Pinch off a piece from the brick (*not* the one you just flattened and shaped) and roll it into a very round ball between your palms. A melonballer may work for this too, and give you a more evenly round ball. Try it and see. Cut the ball in half, put the hemisphere where you want it you want the on the polygon. Repeat until you have the buckle looking like you want it, then bake according to instructions. Once cooled, apply multiple coats of metallic paint, allowing the buckle to dry thoroughly between each coat. Caveat: expect to have to do some experimentation to get satisfactory results. I’ve never worn a buckle made in this fashion, so I don’t know how well it would hold up.
Whatever method and materials you go with, I hope you will report back in with the details and the results.