If you have a model
STL, 3MF, STEP or OBJ. Tell us the material and how many. If a specific
face has to be smooth or a specific hole has to fit a real part, say which —
that changes how we orient it on the plate.
If you have a drawing
A sketch with dimensions is plenty. Photos work too if there's a ruler or
a coin in frame for scale. We'll quote the modeling separately so you can see
what each half costs.
If you have the broken part
Photograph it from several angles with a ruler beside it, and measure
anything that has to mate with something else. Most discontinued parts are
recreatable from that alone.