As above, for that shape, cast iron is cheap in production quantities.
Have a good look at where it fits as a simple circular shape is a lot less work to make. Look at its function; do not slavishly copy its form.
If it does need to be that tri-lobed shape, maybe a laser or plasma cut blank would be a good place to start. Make a dimensioned pencil sketch of it and someone would turn it into a dxf file that could be sent to a cutter. All you would have to do is drill and ream for the three pins and bore and keyway the centre.