Make a pattern out of wax, wood, iron and take it to a fine art casting foundry. Have them give you a bid on the rubber mold, then get some of there wax, we used a wax called victory brown, much easer to work on than paraffin and pour them your self at home using a electric roster oven to melt the wax in, don' use your wife's roster oven it will ruin it, use your mother in laws, if your a blacksmith she dose not like you anyway.
After you get all of the key blanks made you can can make them each unique by carving names or what ever in the wax. then take them back to the foundry and have them cast in silicon bronze. It wont be cheep.
I know because I worked in a art foundry for 14 years before I went to blacksmithing full time 10 years ago.
Chuck