Ferrous metals casting

I need to have a part made with ferrous metal so that I can use a magnet on it. Does anyone know of a foundry in the USA that will do small one off castings from my print? Thank you.

Find a local backyard foundry forum and ask there, much more chances of getting good availability and prices for a one-off than in a “proper” foundry.

That depends on what you need to be done of course. In that regard, can’t you design a space to fit a steel washer or something in the part ? You can probably make a slot in the part, fil it with resin which will be cured with a 405nm laser.