I had the same problem last year and bought a couple of these (which may be the ones you are also looking at):
http://www.ebay.com/itm/22mm-Bronze-...item3f20d75c94
They seem to be well made, although very chunky (I had a little difficulty getting the screw bar to fit through my strap at first) - and I imagine that the bronze is the 'real thing', although I haven't chemically analysed it!! I have also bought a bronze buckle from Benarus (very nice, but with 'Benarus' engraved on it), and have heard some good reports on the Olivier Watch Company buckles, although I haven't seen them in real life:
http://olivierwatches.com/bronze-buckles/
Or, if you just want the 'colour' without the potential patina, you could try something like this:
http://www.ebay.co.uk/itm/2809710079...84.m1423.l2649
I think that the pricing of the solid bronze buckles is about the same all round (US$50 to US$80 plus postage, etc.) so it's whatever takes your fancy really, I suppose.