I think it was in a Trend routing catalogue that I saw the Rosette cutter years ago, no idea if it's still available. It took the job of producing them from a skilled person to one that operates a machine! But all you get is the one shape it cuts.
Steve, you said you made them for 'Fire Surrounds', I can see that and as long as they match, any pair would do, but I know them more for the Georgian doors and presumably other Georgian architraves.
I’ve not looked closely enough to see if they are all the same or if there are local, regional or even turner specific designs. I would imagine there will always be a small market for reproduction parts to match the existing architrave in a house restoration project.