Our shop used to use precast “plants “ that were cast in rubber mold with wood flour and hide glue.
Before that, they were made with wood flour and linseed oil which was baked in an autoclave. A similar process was made to produce linoleum.
Nowadays CNC reproduction has gained part of the market, as has urethane casting.
Many plants can still be bought through millword suppliers.
One such place is Van Dykes restorers.
Here’s a Capital on the same theme as the one you showed. There are probably other sizes and styles available.
Yours looks like two plants, the ionic capital and the surface decoration under it. The piece over the capital might be a third casting.
Sometimes you can approximate an existing piece by literally cutting and pasting existing purchased pieces..