Dunno where to find round ones like that, most (as you probably know) are rectangular or diamond shaped. You can take one to a good bronze foundry and they will make a pattern and make more for you. We did this with a foundry in San Diego, CA (Um, National City Foundry) and had them use the original for a pattern since we didn't care if the size (after casting is a bit smaller) was not perfectly the same. That was very inexpensive in bronze. You would have to have the bronze chrome plated in your case, I suppose. In the USA, Port Townsend Foundry has many patterns already and may have the one you seek.