Call a concrete contractor that does residential work. You will see their ads in the newspaper or go to the lumber yards or concrete mixing plant and ask for names and phone numbers. A stair is a small amount of work, so look around for other concrete projects you will want ( big patio, sidewalk, garage foundation, car servicing pit) and get it all because it will be cheaper. Or, if the stair is all, then the concrete guy may want to furnish a pre-made stair that is bought at the lumber yard and put it on a simple concrete block foundation. You will have to figure out what to do about handrails. If you are going the pre-made concrete route, why don't you have it made from lumber? If you are planning on doing the work yourself, have some big friends to help. You first problem is knowing how to make the concrete forms and in particular the rise and tread of the steps. Being off just a little bit will make the steps awkward. The job will be too small to get a concrete truck, so you will be mixing on site. Which means you will be hauling in materials on a trailer and wheel barrow it over to the stair forms. This is not something for the novice to try.